An acronym is a word or name formed as a type of abbreviation from the initial components of a phrase or a word,

There are no universal standards for the multiple names for such abbreviations or for their orthographic styling. Acronyms result from a word formation process known as blending, in which parts of two or more words are combined to form a new word.

Acronyms flourished especially from the 20th century onwards; the distinction between abbreviation and acronym has been steadily eroded and acronym is commonly used for several types of abbreviation.

Whereas an abbreviation may be any type of shortened form, such as words with the middle omitted (for example, Rd for road or Dr for Doctor), an acronym is a word formed from the first letter or first few letters of each word in a phrase (such as sonar, created from sound navigation and ranging). Attestations for Akronym in German are known from 1921, and for acronym in English from 1940.^[2]

Although the word acronym is often used to refer to any abbreviation formed from initial letters,^[3] some dictionaries and usage commentators define acronym to mean an abbreviation that is pronounced as a word,^[19] in contrast to an initialism (or alphabetism)‍—‌an abbreviation formed from a string of initials (and possibly pronounced as individual letters).^[20] Some dictionaries include additional senses equating acronym with initialism.^[21][22][23] The distinction, when made, hinges on whether the abbreviation is pronounced as a word or as a string of individual letters. Examples in reference works that make the distinction include "NATO" /ˈneɪtoʊ/, "scuba" /ˈskuːbə/, and "radar" /ˈreɪdɑːr/ for acronyms; and "FBI" /ˌɛfˌbiːˈaɪ/, "CRT" /ˌsiːˌɑːrˈtiː/, and "HTML" /ˌeɪtʃˌtiːˌɛmˈɛl/ for initialisms.^{[4][16][24][25]} The rest of this article uses acronym for both types of abbreviation.

The distinction is not well-maintained. According to Merriam-Webster's Dictionary of English Usage:^[3] "A number of commentators ... believe that acronyms can be differentiated from other abbreviations in being pronounceable as words. Dictionaries, however, do not make this distinction because writers in general do not. ... Initialism, an older word than acronym, seems to be too little known to the general public to serve as the customary term standing in contrast with acronym in a narrow sense." About the use of acronym to only mean those pronounced as words, Fowler's Modern English Usage (3rd ed.) states:^[26] "The limitations of the term being not widely known to the general public, acronym is also often applied to abbreviations that are familiar but are not pronounceable as words. ... Such terms are also called initialisms."

A clearer distinction has also been drawn by Pyles & Algeo (1970),^[3] who divided acronyms as a general category into word acronyms pronounced as words, and initialisms sounded out as letters.

There is no special term for abbreviations whose pronunciation involves the combination of letter names and words or word-like pronunciations of strings of letters, such as "JPEG" /ˈdʒeɪpɛɡ/ and "MS-DOS" /ˌɛmɛsˈdɒs/. There is also some disagreement as to what to call abbreviations that some speakers pronounce as letters and others pronounce as a word. For example, the terms "URL" and "IRA" can be pronounced as individual letters: /ˌjuːˌɑːrˈɛl/ and /ˌaɪˌɑːrˈeɪ/, respectively; or as a single word: /ɜːrl/ and /ˈaɪrə/, respectively.

The spelled-out form of an acronym or initialism (that is, what it stands for) is called its expansion.

Acronymy, like retronymy, is a linguistic process that has existed throughout history but for which there was little to no naming, conscious attention, or systematic analysis until relatively recent times. Like retronymy, it became much more common in the 20th century than it had formerly been.

Ancient examples of acronymy (regardless of whether there was metalanguage at the time to describe it) include the following:

During the mid- to late 19th century, an acronym-disseminating trend spread through the American and European business communities: abbreviating corporation names —such as on the sides of railroad cars (e.g., "Richmond, Fredericksburg and Potomac Railroad" → "RF&P"); on the sides of barrels and crates; and on ticker tape and in the small-print newspaper stock listings that got their data from it (e.g. American Telephone and Telegraph Company → AT&T). Some well-known commercial examples dating from the 1890s through 1920s include "Nabisco" ("National Biscuit Company"),^[32] "Esso" (from "S.O.", from "Standard Oil"), and "Sunoco" ("Sun Oil Company").

Another driver for the adoption of acronyms was modern warfare, with its many highly technical terms. While there is no recorded use of military acronyms in documents dating from the American Civil War (acronyms such as "ANV" for "Army of Northern Virginia" post-date the war itself), they had become somewhat common in World War I and were very much a part even of the vernacular language of the soldiers during World War II,^[33] who themselves were referred to as G.I.s.

The widespread, frequent use of acronyms across the whole range of registers is a relatively new linguistic phenomenon in most languages, becoming increasingly evident since the mid-20th century. As literacy rates rose, and as advances in science and technology brought with them a constant stream of new (and sometimes more complex) terms and concepts, the practice of abbreviating terms became increasingly convenient. The Oxford English Dictionary (OED) records the first printed use of the word initialism as occurring in 1899, but it did not come into general use until 1965, well after acronym had become common.

By 1943, the term acronym had been used in English to recognize abbreviations (and contractions of phrases) that were pronounced as words.^[32] (It was formed from the Greek words ἄκρος, akros, "topmost, extreme" and ὄνομα, onoma, "name.") For example, the army offense of being absent without official leave was abbreviated to "A.W.O.L." in reports, but when pronounced as a word (awol), it became an acronym.^[34] While initial letters are commonly used to form an acronym, the original definition was "a word made from the initial letters or syllables of other words",^[35] for example UNIVAC from UNIVersal Automatic Computer.^[36]

In English, acronyms pronounced as words may be a 20th-century phenomenon. Linguist David Wilton in Word Myths: Debunking Linguistic Urban Legends claims that "forming words from acronyms is a distinctly twentieth- (and now twenty-first-) century phenomenon. There is only one known pre-twentieth-century [English] word with an acronymic origin and it was in vogue for only a short time in 1886. The word is colinderies or colinda, an acronym for the Colonial and Indian Exposition held in London in that year."^[37][38] However, although acronymic words seem not to have been employed in general vocabulary before the 20th century (as Wilton points out), the concept of their formation is treated as effortlessly understood (and evidently not novel) in a Poe story of the 1830s, "How to Write a Blackwood Article", which includes the contrived acronym "P.R.E.T.T.Y.B.L.U.E.B.A.T.C.H.".

The use of Latin and Neo-Latin terms in vernaculars has been pan-European and predates modern English. Some examples of acronyms in this class are:

The earliest example of a word derived from an acronym listed by the OED is "abjud" (now "abjad"), formed from the original first four letters of the Arabic alphabet in the late 18th century.^[39] Some acrostics predate this, however, such as the Restoration witticism arranging the names of some members of Charles II's Committee for Foreign Affairs to produce the "CABAL" ministry.^[40]

Acronyms are used most often to abbreviate names of organizations and long or frequently referenced terms. The armed forces and government agencies frequently employ acronyms; some well-known examples from the United States are among the "alphabet agencies" (also jokingly referred to as "alphabet soup") created by Franklin D. Roosevelt (also of course known as "FDR") under the New Deal. Business and industry also are prolific coiners of acronyms. The rapid advance of science and technology in recent centuries seems to be an underlying force driving the usage, as new inventions and concepts with multiword names create a demand for shorter, more manageable names. One representative example, from the U.S. Navy, is "COMCRUDESPAC", which stands for "commander, cruisers destroyers Pacific"; it is also seen as "ComCruDesPac". "YABA-compatible" (where "YABA" stands for "yet another bloody acronym") is used to mean that a term's acronym can be pronounced but is not an offensive word, e.g. "When choosing a new name, be sure it is 'YABA-compatible'."^[41]

Acronym use has been further popularized by text messaging on mobile phones with short message service (SMS), and instant messenger (IM). To fit messages into the 160-character SMS limit, and to save time, acronyms such as "GF" ("girlfriend"), "LOL" ("laughing out loud"), and "DL" ("download" or "down low") have become popular.^[42] Some prescriptivists disdain texting acronyms and abbreviations as decreasing clarity, or as failure to use "pure" or "proper" English. Others point out that language change has happened for thousands of years, and argue that it should be embraced as inevitable, or as innovation that adapts the language to changing circumstances. In this view, the modern practice is just as legitimate as those in "proper" English of the current generation of speakers, such as the abbreviation of corporation names in places with limited writing space (e.g., ticker tape, newspaper column inches).

In formal writing for a broad audience, the expansion is typically given at the first occurrence of the acronym within a given text, for the benefit of those readers who do not know what it stands for. The capitalization of the original term is independent of it being acronymized, being lowercase for a common noun such as frequently asked questions (FAQ) but uppercase for a proper noun such as the United Nations (UN) (as explained at Case > Casing of expansions).

In addition to expansion at first use, some publications also have a key listing all the acronyms used they have used and what their expansions are. This is a convenience for readers for two reasons. The first is that if they are not reading the entire publication sequentially (which is a common mode of reading), then they may encounter an acronym without having seen its expansion. Having a key at the start or end of the publication obviates skimming over the text searching for an earlier use to find the expansion. (This is especially important in the print medium, where no search utility is available.) The second reason for the key feature is its pedagogical value in educational works such as textbooks. It gives students a way to review the meanings of the acronyms introduced in a chapter after they have done the line-by-line reading, and also a way to quiz themselves on the meanings (by covering up the expansion column and recalling the expansions from memory, then checking their answers by uncovering). In addition, this feature enables readers possessing knowledge of the abbreviations not to have to encounter expansions (redundant for such readers).

Expansion at first use and the abbreviation-key feature are aids to the reader that originated in the print era, but they are equally useful in print and online. In addition, the online medium offers yet more aids, such as tooltips, hyperlinks, and rapid search via search engine technology.

Acronyms often occur in jargon. An acronym may have different meanings in different areas of industry, writing, and scholarship. The general reason for this is convenience and succinctness for specialists, although it has led some to obfuscate the meaning either intentionally, to deter those without such domain-specific knowledge, or unintentionally, by creating an acronym that already existed.

The medical literature has been struggling to control the proliferation of acronyms as their use has evolved from aiding communication to hindering it. This has become such a problem that it is even evaluated at the level of medical academies such as the American Academy of Dermatology. ^[43]

Acronyms are often taught as mnemonic devices, for example in physics the colors of the visible spectrum are said to be "ROY G. BIV" ("red-orange-yellow-green-blue-indigo-violet"). They are also used as mental checklists, for example in aviation: "GUMPS", which is "gas-undercarriage-mixture-propeller-seatbelts". Other examples of mnemonic acronyms are "CAN SLIM", and "PAVPANIC" as well as "PEMDAS".

It is not uncommon for acronyms to be cited in a kind of false etymology, called a folk etymology, for a word. Such etymologies persist in popular culture but have no factual basis in historical linguistics, and are examples of language-related urban legends. For example, "cop" is commonly cited as being derived, it is presumed, from "constable on patrol",^[44] and "posh" from "port outward, starboard home".^[45] With some of these specious expansions, the "belief" that the etymology is acronymic has clearly been tongue-in-cheek among many citers, as with "gentlemen only, ladies forbidden" for "golf", although many other (more credulous) people have uncritically taken it for fact.^[45][46] Taboo words in particular commonly have such false etymologies: "shit" from "ship/store high in transit"^[37][47] or "special high-intensity training" and "fuck" from "for unlawful carnal knowledge", or "fornication under consent/command of the king".^[47]

In English, abbreviations have traditionally been written with a full stop/period/point in place of the deleted part to show the ellipsis of letters—although the colon and apostrophe have also had this role—and with a space after full stops (e.g. "A. D."). In the case of most acronyms, each letter is an abbreviation of a separate word and, in theory, should get its own termination mark. Such punctuation is diminishing with the belief that the presence of all-capital letters is sufficient to indicate that the word is an abbreviation.^[48]

Some influential style guides, such as that of the BBC, no longer require punctuation to show ellipsis; some even proscribe it. Larry Trask, American author of The Penguin Guide to Punctuation, states categorically that, in British English, "this tiresome and unnecessary practice is now obsolete."^[49]

Nevertheless, some influential style guides, many of them American, still require periods in certain instances. For example, The New York Times Manual of Style and Usage recommends following each segment with a period when the letters are pronounced individually, as in "K.G.B.", but not when pronounced as a word, as in "NATO".^[50] The logic of this style is that the pronunciation is reflected graphically by the punctuation scheme.

When a multiple-letter abbreviation is formed from a single word, periods are in general not used, although they may be common in informal usage. "TV", for example, may stand for a single word ("television" or "transvestite", for instance), and is in general spelled without punctuation (except in the plural). Although "PS" stands for the single word "postscript" (or the Latin postscriptum), it is often spelled with periods ("P.S.").

The slash ('/', or solidus) is sometimes used to separate the letters in a two-letter acronym, as in "N/A" ("not applicable, not available"), "c/o" ("care of") and "w/o" ("without").

Inconveniently long words used frequently in related contexts can be represented according to their letter count. For example, "i18n" abbreviates "internationalization", a computer-science term for adapting software for worldwide use. The "18 represents the 18 letters that come between the first and the last in "internationalization". "Localization" can be abbreviated "l10n", "multilingualization" "m17n", and "accessibility" "a11y". In addition to the use of a specific number replacing that many letters, the more general "x" can be used to replace an unspecified number of letters. Examples include "Crxn" for "crystallization" and the series familiar to physicians for history, diagnosis, and treatment ("hx", "dx", "tx").

There is a question about how to pluralize acronyms. Often a writer will add an 's' following an apostrophe, as in "PC's". However, Kate Turabian, writing about style in academic writings,^[51] allows for an apostrophe to form plural acronyms "only when an abbreviation contains internal periods or both capital and lowercase letters". Turabian would therefore prefer "DVDs" and "URLs" and "Ph.D.'s". The Modern Language Association^[52] and American Psychological Association^[53][54] prohibit apostrophes from being used to pluralize acronyms regardless of periods (so "compact discs" would be "CDs" or "C.D.s"), whereas The New York Times Manual of Style and Usage requires an apostrophe when pluralizing all abbreviations regardless of periods (preferring "PC's, TV's and VCR's").^[55]

Possessive plurals that also include apostrophes for mere pluralization and periods appear especially complex: for example, "the C.D.'s' labels" (the labels of the compact discs). In some instances, however, an apostrophe may increase clarity: for example, if the final letter of an abbreviation is "S", as in "SOS's" (although abbreviations ending with S can also take "-es", e.g. "SOSes"), or when pluralizing an abbreviation that has periods.^[56][57]

A particularly rich source of options arises when the plural of an acronym would normally be indicated in a word other than the final word if spelled out in full. A classic example is "Member of Parliament", which in plural is "Members of Parliament". It is possible then to abbreviate this as "M's P".^[58][59] (or similar^[60]), as used by former Australian Prime Minister Ben Chifley.^[61][62][63] This usage is less common than forms with "s" at the end, such as "MPs", and may appear dated or pedantic. In common usage, therefore, "weapons of mass destruction" becomes "WMDs", "prisoners of war" becomes "POWs", and "runs batted in" becomes "RBIs".^[64]

The argument that acronyms should have no different plural form (for example, "If D can stand for disc, it can also stand for discs") is in general disregarded because of the practicality in distinguishing singulars and plurals. This is not the case, however, when the abbreviation is understood to describe a plural noun already: For example, "U.S." is short for "United States", but not "United State". In this case, the options for making a possessive form of an abbreviation that is already in its plural form without a final "s" may seem awkward: for example, "U.S.", "U.S.'s", etc. In such instances, possessive abbreviations are often forgone in favor of simple attributive usage (for example, "the U.S. economy") or expanding the abbreviation to its full form and then making the possessive (for example, "the United States' economy"). On the other hand, in speech, the pronunciation "United States's" sometimes is used.

Abbreviations that come from single, rather than multiple, words—such as "TV" ("television")—are usually pluralized without apostrophes ("two TVs"); most writers feel that the apostrophe should be reserved for the possessive ("the TV's antenna").

In some languages, the convention of doubling the letters in the acronym is used to indicate plural words: for example, the Spanish EE. UU., for Estados Unidos ('United States'). This old convention is still followed for a limited number of English abbreviations, such as SS. for "Saints", pp. for the Latin plural of "pages", paginae, or MSS for "manuscripts". In the case of pp. it derives from the original Latin phrase "per procurationem" meaning 'through the agency of';^[65] an English translation alternative is particular pages in a book or document: see pp. 8–88.^[66]

The most common capitalization scheme seen with acronyms is all-uppercase (all-caps), except for those few that have linguistically taken on an identity as regular words, with the acronymous etymology of the words fading into the background of common knowledge, such as has occurred with the words "scuba", "laser", and "radar"—these are known as anacronyms.^[67] Anacronyms (note well -acro-) should not be homophonously confused with anachronyms (note well -chron-), which are a type of misnomer.

Small caps are sometimes used to make the run of capital letters seem less jarring to the reader. For example, the style of some American publications, including the Atlantic Monthly and USA Today, is to use small caps for acronyms longer than three letters; thus "U.S." and "FDR" in normal caps, but "nato" in small caps. The acronyms "AD" and "BC" are often smallcapped as well, as in: "From 4004 bc to ad 525".

Words derived from an acronym by affixing are typically expressed in mixed case, so the root acronym is clear. For example, "pre-WWII politics", "post-NATO world", "DNAase". In some cases a derived acronym may also be expressed in mixed case. For example, "messenger RNA" and "transfer RNA" become "mRNA" and "tRNA".

Some publications choose to capitalize only the first letter of acronyms, reserving all-caps styling for initialisms, writing the pronounced acronyms "Nato" and "Aids" in mixed case, but the initialisms "USA" and "FBI" in all caps. For example, this is the style used in The Guardian,^[68] and BBC News typically edits to this style (though its official style guide, dating from 2003, still recommends all-caps^[69]). The logic of this style is that the pronunciation is reflected graphically by the capitalization scheme.

Some style manuals also base the letters' case on their number. The New York Times, for example, keeps "NATO" in all capitals (while several guides in the British press may render it "Nato"), but uses lower case in "UNICEF" (from "United Nations International Children's Emergency Fund") because it is more than four letters, and to style it in caps might look ungainly (flirting with the appearance of "shouting capitals").

While abbreviations typically exclude the initials of short function words (such as "and", "or", "of", or "to"), this is not always the case. (A similar set of words is sometimes left as lowercase in headers and publication titles.) Sometimes function words are included to make a pronounceable acronym, such as CORE (Congress of Racial Equality). Sometimes the letters representing these words are written in lower case, such as in the cases of "TfL" ("Transport for London") and LotR (Lord of the Rings); this usually occurs when the acronym represents a multi-word proper noun.

Numbers (both cardinal and ordinal) in names are often represented by digits rather than initial letters: as in "4GL" ("fourth generation language") or "G77" ("Group of 77"). Large numbers may use metric prefixes, as with "Y2K" for "Year 2000" (sometimes written "Y2k", because the SI symbol for 1000 is "k"—not "K", which stands for "kelvin"). Exceptions using initials for numbers include "TLA" ("three-letter acronym/abbreviation") and "GoF" ("Gang of Four"). Abbreviations using numbers for other purposes include repetitions, such as "W3C" ("World Wide Web Consortium") and T3 (Trends, Tips & Tools for Everyday Living); pronunciation, such as "B2B" ("business to business"); and numeronyms, such as "i18n" ("internationalization"; "18" represents the 18 letters between the initial "i" and the final "n").

Although many authors of expository writing show a predisposition to capitalizing the initials of the expansion for pedagogical emphasis (trying to thrust the reader's attention toward where the letters are coming from), this sometimes conflicts with the convention of English orthography, which reserves capitals in the middle of sentences for proper nouns. Enforcing the general convention, most professional editors case-fold such expansions to their standard orthography when editing manuscripts for publication. The justification is that (1) readers are smart enough to figure out where the letters came from, even without their being capitalized for emphasis, and that (2) common nouns do not take capital initials in standard English orthography. Such house styles also usually disfavor bold or italic font for the initial letters. For example, "the onset of Congestive Heart Failure (CHF)" or "the onset of congestive heart failure (CHF)" if found in an unpublished manuscript would be rewritten as "the onset of congestive heart failure (CHF)" in the final published article when following the AMA Manual of Style.^[70]

Some apparent acronyms or other abbreviations do not stand for anything and cannot be expanded to some meaning. Such pseudo-acronyms may be pronunciation-based, such as "BBQ" (bee-bee-cue), for "barbecue", or "K9" (kay-nine) for "canine". Pseudo-acronyms also frequently develop as "orphan initialisms"; an existing acronym is redefined as a non-acronymous name, severing its link to its previous meaning.^[71][72] For example, the letters of the "SAT", a US college entrance test originally dubbed "Scholastic Aptitude Test", no longer officially stand for anything.^[73][74]

This is common with companies that want to retain brand recognition while moving away from an outdated image: American Telephone and Telegraph became AT&T,^[71] "Kentucky Fried Chicken" became "KFC" to de-emphasize the role of frying in the preparation of its signature dishes,^[75][1] and British Petroleum became BP.^[72][76] Russia Today has rebranded itself as RT. American Movie Classics has simply rebranded itself as AMC. "Genzyme Transgenics Corporation" became "GTC Biotherapeutics, Inc." in order to reduce perceived corporate risk of sabotage/vandalism by Luddite activists. The Learning Channel became TLC following its move towards reality series involving lifestyles, family life, and personal stories, and American District Telegraph became simply known as ADT.

Pseudo-acronyms may have advantages in international markets: for example, some national affiliates of International Business Machines are legally incorporated as "IBM" (for example, "IBM Canada") to avoid translating the full name into local languages. Likewise, "UBS" is the name of the merged Union Bank of Switzerland and Swiss Bank Corporation,^[77] and "HSBC" has replaced "The Hongkong and Shanghai Banking Corporation." Sometimes, companies whose original name gives a clear indication of their place of origin will use acronyms when expanding to foreign markets—for example, Toronto-Dominion Bank continues to operate under the full name in Canada, but its U.S. subsidiary is known as "TD Bank", just as Royal Bank of Canada used its full name in Canada (a constitutional monarchy), but its now-defunct U.S. subsidiary was called "RBC Bank".

Rebranding can lead to redundant acronym syndrome, as when Trustee Savings Bank became TSB Bank, or when Railway Express Agency became "REA Express". A few high-tech companies have taken the redundant acronym to the extreme: for example, ISM Information Systems Management Corp. and SHL Systemhouse Ltd. Examples in entertainment include the television shows CSI: Crime Scene Investigation and Navy: NCIS ("Navy" was dropped in the second season), where the redundancy was likely designed to educate new viewers as to what the initials stood for. The same reasoning was in evidence when the Royal Bank of Canada's Canadian operations rebranded to RBC Royal Bank, or when Bank of Montreal rebranded their retail banking subsidiary BMO Bank of Montreal.

Another common example is "RAM memory", which is redundant because "RAM" ("random-access memory") includes the initial of the word "memory". "PIN" stands for "personal identification number", obviating the second word in "PIN number"; in this case its retention may be motivated to avoid ambiguity with the homophonous word "pin". Other examples include "ATM machine", "EAB bank", "CableACE Award", "DC Comics", "HIV virus", Microsoft's NT Technology, and the formerly redundant "SAT test", now simply "SAT Reasoning Test"). TNN (The Nashville/National Network) also renamed itself "The New TNN" for a brief interlude.

Sometimes, the initials continue to stand for an expanded meaning, but the original meaning is simply replaced. Some examples:

A backronym (or bacronym) is a phrase that is constructed "after the fact" from a previously existing word. For example, the novelist and critic Anthony Burgess once proposed that the word "book" ought to stand for "box of organized knowledge".^[78] A classic real-world example of this is the name of the predecessor to the Apple Macintosh, The Apple Lisa, which was said to refer to "Local Integrated Software Architecture", but was actually named after Steve Jobs's daughter, born in 1978.

Backronyms are oftentimes used to comedic effect. An example of creating a backronym for comedic effect would be in naming a group or organization, the name "A.C.R.O.N.Y.M" stands for (among other things) "a clever regiment of nerdy young men".

Acronyms are sometimes contrived, that is, deliberately designed to be especially apt for the thing being named (by having a dual meaning or by borrowing the positive connotations of an existing word). Some examples of contrived acronyms are USA PATRIOT, CAN SPAM, CAPTCHA and ACT UP. The clothing company French Connection began referring to itself as fcuk, standing for "French Connection United Kingdom." The company then created T-shirts and several advertising campaigns that exploit the acronym's similarity to the taboo word "fuck".

The US Department of Defense's Defense Advanced Research Projects Agency (DARPA) is known for developing contrived acronyms to name projects, including RESURRECT, NIRVANA, and DUDE. In July 2010, *Wired * magazine reported that DARPA announced programs to "..transform biology from a descriptive to a predictive field of science" named BATMAN and ROBIN for "Biochronicity and Temporal Mechanisms Arising in Nature" and "Robustness of Biologically-Inspired Networks",^[79] a reference to the Batman and Robin comic-book superheroes.

The short-form names of clinical trials and other scientific studies constitute a large class of acronyms that includes many contrived examples, as well as many with a partial rather than complete correspondence of letters to expansion components. These trials tend to have full names that are accurately descriptive of what the trial is about but are thus also too long to serve practically as names within the syntax of a sentence, so a short name is also developed, which can serve as a syntactically useful handle and also provide at least a degree of mnemonic reminder as to the full name. Examples widely known in medicine include the ALLHAT trial (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial) and the CHARM trial (Candesartan in Heart Failure: Assessment of Reduction in Mortality and Morbidity). The fact that RAS syndrome is often involved, as well as that the letters often don't entirely match, have sometimes been pointed out by annoyed researchers preoccupied by the idea that because the archetypal form of acronyms originated with one-to-one letter matching, there must be some moral impropriety in their ever deviating from that form. However, the raison d'être of clinical trial acronyms, as with gene and protein symbols, is simply to have a syntactically usable and recallable short name to complement the long name that is often syntactically unusable and not memorized. It is useful for the short name to give a reminder of the long name, which supports the reasonable censure of "cutesy" examples that provide little to no hint of it. But beyond that reasonably close correspondence, the short name's chief utility is in functioning cognitively as a name, rather than being a cryptic and forgettable string, albeit faithful to the matching of letters. However, other reasonable critiques have been (1) that it is irresponsible to mention trial acronyms without explaining them at least once by providing the long names somewhere in the document,^[80] and (2) that the proliferation of trial acronyms has resulted in ambiguity, such as 3 different trials all called ASPECT, which is another reason why failing to explain them somewhere in the document is irresponsible in scientific communication.^[80] At least one study has evaluated the citation impact and other traits of acronym-named trials compared with others,^[81] finding both good aspects (mnemonic help, name recall) and potential flaws (connotatively driven bias).^[81]

Some acronyms are chosen deliberately to avoid a name considered undesirable: For example, Verliebt in Berlin (ViB), a German telenovela, was first intended to be Alles nur aus Liebe (All for Love), but was changed to avoid the resultant acronym ANAL. Likewise, the Computer Literacy and Internet Technology qualification is known as CLaIT,^[82] rather than CLIT. In Canada, the Canadian Conservative Reform Alliance (Party) was quickly renamed to the "Canadian Reform Conservative Alliance" when its opponents pointed out that its initials spelled CCRAP (pronounced "see crap"). (The satirical magazine Frank had proposed alternatives to CCRAP, namely SSHIT and NSDAP.) Two Irish Institutes of Technology (Galway and Tralee) chose different acronyms from other institutes when they were upgraded from Regional Technical colleges. Tralee RTC became the Institute of Technology Tralee (ITT), as opposed to Tralee Institute of Technology (TIT). Galway RTC became Galway-Mayo Institute of Technology (GMIT), as opposed to Galway Institute of Technology (GIT). The charity sports organization Team in Training is known as "TNT" and not "TIT". Technological Institute of Textile & Sciences is still known as "TITS". George Mason University was planning to name their law school the "Antonin Scalia School of Law" (ASSOL) in honor of the late Antonin Scalia, only to change it to the "Antonin Scalia Law School" later.^[83]

A macronym, or nested acronym, is an acronym in which one or more letters stand for acronyms (or abbreviations) themselves. The word "macronym" is a portmanteau of "macro-" and "acronym".

Some examples of macronyms are:

Some macronyms can be multiply nested: the second-order acronym points to another one further down a hierarchy. In an informal competition run by the magazine New Scientist, a fully documented specimen was discovered that may be the most deeply nested of all: RARS is the "Regional ATOVS Retransmission Service"; ATOVS is "Advanced TOVS"; TOVS is "TIROS operational vertical sounder"; and TIROS is "Television infrared observational satellite".^[84] Fully expanded, "RARS" might thus become "Regional Advanced Television Infrared Observational Satellite Operational Vertical Sounder Retransmission Service".

Another example is VITAL, which expands to "VHDL Initiative Towards ASIC Libraries" (a total of 15 words when fully expanded).

However, to say that "RARS" stands directly for that string of words, or can be interchanged with it in syntax (in the same way that "CHF" can be usefully interchanged with "congestive heart failure"), is a prescriptive misapprehension rather than a linguistically accurate description; the true nature of such a term is closer to anacronymic than to being interchangeable like simpler acronyms are. The latter are fully reducible in an attempt to "spell everything out and avoid all abbreviations," but the former are irreducible in that respect; they can be annotated with parenthetical explanations, but they cannot be eliminated from speech or writing in any useful or practical way. Just as the words laser and radar function as words in syntax and cognition without a need to focus on their acronymic origins, terms such as "RARS" and "CHA2DS2–VASc score" are irreducible in natural language; if they are purged, the form of language that is left may conform to some imposed rule, but it cannot be described as remaining natural. Similarly, protein and gene nomenclature, which uses symbols extensively, includes such terms as the name of the NACHT protein domain, which reflects the symbols of some proteins that contain the domain—NAIP (NLR family apoptosis inhibitor protein), C2TA (major histocompatibility complex class II transcription activator), HET-E (incompatibility locus protein from Podospora anserine), and TP1 (telomerase-associated protein)—but is not syntactically reducible to them. The name is thus itself more symbol than acronym, and its expansion cannot replace it while preserving its function in natural syntax as a name within a clause clearly parsable by human readers or listeners.

A special type of macronym, the recursive acronym, has letters whose expansion refers back to the macronym itself. One of the earliest examples appears in The Hacker's Dictionary as MUNG, which stands for "MUNG Until No Good".

Some examples of recursive acronyms are:

In English language discussions of languages with syllabic or logographic writing systems (such as Chinese, Japanese, and Korean), "acronyms" describe the short forms that take selected characters from a multi-character word.

For example, in Chinese, "university" (大學/大学, literally "great learning") is usually abbreviated simply as 大 ("great") when used with the name of the institute. So "Peking University" (北京大学) is commonly shortened to 北大 (lit. "north-great") by also only taking the first character of Peking, the "northern capital" (北京; Beijing). In some cases, however, other characters than the first can be selected. For example, the local short form of "Hong Kong University" (香港大學) uses "Kong" (港大) rather than "Hong".

There are also cases where some longer phrases are abbreviated drastically, especially in Chinese politics, where proper nouns were initially translated from Soviet Leninist terms. For instance, the full name of China's highest ruling council, the Politburo Standing Committee (PSC), is "Standing Committee of the Central Political Bureau of the Communist Party of China" (中国共产党中央政治局常务委员会). The term then reduced the "Communist Party of China" part of its name through acronyms, then the "Standing Committee" part, again through acronyms, to create "中共中央政治局常委". Alternatively, it omitted the "Communist Party" part altogether, creating "Politburo Standing Committee" (政治局常委会), and eventually just "Standing Committee" (常委会). The PSC's members full designations are "Member of the Standing Committee of the Central Political Bureau of the Communist Party of China" (中国共产党中央政治局常务委员会委员); this was eventually drastically reduced to simply Changwei (常委), with the term Ruchang (入常) used increasingly for officials destined for a future seat on the PSC. In another example, the word "全国人民代表大会" (National People's Congress) can be broken into four parts: "全国" = "the whole nation", "人民" = "people", "代表" = "representatives", "大会" = "conference". Yet, in its short form "人大" (literally "man/people big"), only the first characters from the second and the fourth parts are selected; the first part ("全国") and the third part ("代表") are simply ignored. In describing such abbreviations, the term initialism is inapplicable.

Many proper nouns become shorter and shorter over time. For example, the CCTV New Year's Gala, whose full name is literally read as "China Central Television Spring Festival Joint Celebration Evening Gala" (中国中央电视台春节联欢晚会) was first shortened to "Spring Festival Joint Celebration Evening Gala" (春节联欢晚会), but eventually referred to as simply Chunwan (春晚). Along the same vein, Zhongguo Zhongyang Dianshi Tai (中国中央电视台) was reduced to Yangshi (央视) in the mid-2000s.

Many aspects of academics in Korea follow similar acronym patterns as Chinese, owing to the two languages' commonalities, like using the word for "big" or "great" i.e. dae (대), to refer to universities (대학; daehak, literally "great learning" although "big school" is an acceptable alternate). They can be interpreted similarly to American university appellations such as, "UPenn" or "Texas Tech."

Some acronyms are shortened forms of the school's name, like how Hongik University (홍익대학교, Hongik Daehakgyo) is shortened to Hongdae (홍대, "Hong, the big [school]" or "Hong-U") Other acronyms can refer to the university's main subject, e.g. Korea National University of Education (한국교원대학교, Hanguk Gyowon Daehakgyo) is shortened to Gyowondae (교원대, "Big Ed." or "Ed.-U"). Other schools use a Koreanized version of their English acronym. The Korea Advanced Institute of Science and Technology (한국과학기술원, Hanguk Gwahak Gisulwon) is referred to as KAIST (카이스트, Kaiseuteu) in both English and Korean. The 3 most prestigious schools in Korea are known as SKY (스카이, seukai), combining the first letter of their English names (Seoul National, Korea, and Yonsei Universities). In addition, the College Scholastic Ability Test (대학수학능력시험, Daehak Suhang Neungryeok Siheom) is shortened to Suneung (수능, "S.A.").

The Japanese language makes extensive use of abbreviations, but only some of these are acronyms.

Chinese-based words (Sino-Japanese vocabulary) uses similar acronym formation to Chinese, like Tōdai (東大) for Tōkyō Daigaku (東京大学, Tokyo University). In some cases alternative pronunciations are used, as in Saikyō for 埼京, from Saitama + Tōkyo (埼玉＋東京), rather than Saitō.

Non-Chinese foreign borrowings (gairaigo) are instead frequently abbreviated as clipped compounds, rather than acronyms, using several initial sounds. This is visible in katakana transcriptions of foreign words, but is also found with native words (written in hiragana). For example, the Pokémon media franchise's name originally stood for "pocket monsters" (ポケット·モンスター [po-ke-tto-mon-su-tā] → ポケモン), which is still the long-form of the name in Japanese, and "wāpuro" stands for "word processor" (ワード·プロセッサー [wā-do-pu-ro-se-ssā]→ ワープロ).

To a greater degree than English does, German tends toward acronyms that use initial syllables rather than initial single letters, although it uses many of the latter type as well. Some examples of the syllabic type are Gestapo rather than GSP (for Geheime Staatspolizei, 'Secret State Police'); Flak rather than FAK (for Fliegerabwehrkanone, anti-aircraft gun); Kripo rather than KP (for Kriminalpolizei, detective division police). The extension of such contraction to a pervasive or whimsical degree has been mockingly labeled Aküfi (for Abkürzungsfimmel, strange habit of abbreviating). Examples of Aküfi include Vokuhila (for vorne kurz, hinten lang, short in the front, long in the back, i.e., a mullet) and the mocking of Adolf Hitler's title as Gröfaz (Größter Feldherr aller Zeiten, "Greatest General of all Times").

It is common to take more than just one initial letter from each of the words composing the acronym; regardless of this, the abbreviation sign gershayim ⟨״⟩ is always written between the second-last and last letters of the non-inflected form of the acronym, even if by this it separates letters of the same original word. Examples (keep in mind Hebrew reads right-to-left): ארה״ב‎ (for ארצות הברית‎, the United States); ברה״מ‎ (for ברית המועצות‎, the Soviet Union); ראשל״צ‎ (for ראשון לציון‎, Rishon LeZion); ביה״ס‎ (for בית הספר‎, the school). An example that takes only the initial letters from its component words is צה״ל‎ (Tzahal, for צבא הגנה לישראל‎, Israel Defense Forces). In inflected forms the abbreviation sign gershayim remains between the second-last and last letters of the non-inflected form of the acronym (e.g. "report", singular: דו״ח‎, plural: דו״חות‎; "squad commander", masculine: מ״כ‎, feminine: מ״כית‎).

There is also a widespread use of acronyms in Indonesia in every aspect of social life. For example, the Golkar political party stands for "Partai Golongan Karya", Monas stands for "Monumen Nasional" (National Monument), the Angkot public transport stands for "Angkutan Kota" (city public transportation), warnet stands for "warung internet" (internet cafe), and many others. Some acronyms are considered formal (or officially adopted), while many more are considered informal, slang or colloquial.

The capital's metropolitan area (Jakarta and its surrounding satellite regions), Jabodetabek, is another infamous acronym. This stands for "Jakarta-Bogor-Depok-Tangerang-Bekasi". Many highways are also named by the acronym method; e.g. Jalan Tol (Toll Road) Jagorawi (Jakarta-Bogor-Ciawi) and Purbaleunyi (Purwakarta-Bandung-Cileunyi), Joglo Semar (Jogja-solo-semarang).

In some languages, especially those that use certain alphabets, many acronyms come from the governmental use, particularly in the military and law enforcement services. The Indonesian military (TNI—Tentara Nasional Indonesia) and Indonesian police (POLRI—Kepolisian Republik Indonesia) are infamous for heavy acronyms use. Examples include the Kopassus (Komando Pasukan Khusus; Special Forces Command), Kopaska (Komando Pasukan Katak; Frogmen Command), Kodim (Komando Distrik Militer; Military District Command—one of the Indonesian army's administrative divisions), Serka (Sersan Kepala; Head Sergeant), Akmil (Akademi Militer; Military Academy—in Magelang) and many other terms regarding ranks, units, divisions, procedures, etc.

Acronyms that use parts of words (not necessarily syllables) are commonplace in Russian as well, e.g. Газпром (Gazprom), for Газовая промышленность (Gazovaya promyshlennost, "gas industry"). There are also initialisms, such as СМИ (SMI, for средства массовой информации sredstva massovoy informatsii, "means of mass informing", i.e.Лаг}} (GULag) combines two initials and three letters of the final word: it stands for Главное управление лагерей (Glavnoe upravlenie lagerey, "Chief Administration of Camps").

Historically, "OTMA" was an acronym sometimes used by the daughters of Emperor Nicholas II of Russia and his consort, Alexandra Feodorovna, as a group nickname for themselves, built from the first letter of each girl's name in the order of their births: "Olga, Tatiana, Maria and Anastasia".

In Swahili, acronyms are common for naming organizations such as "TUKI", which stands for Taasisi ya Uchunguzi wa Kiswahili (the Institute for Swahili Research). Multiple initial letters (often the initial syllable of words) are often drawn together, as seen more in some languages than others.

In Vietnamese, which has an abundance of compound words, initialisms are very commonly used for both proper and common nouns. Examples include TP.HCM (Thành phố Hồ Chí Minh, Ho Chi Minh City), THPT (trung học phổ thông, high school), CLB (câu lạc bộ, club), CSDL (cơ sở dữ liệu, database), NXB (nhà xuất bản, publisher), ÔBACE (ông bà anh chị em, a general form of address), and CTTĐVN (các Thánh tử đạo Việt Nam, Vietnamese Martyrs). Longer examples include CHXHCNVN (Cộng hòa Xã hội chủ nghĩa Việt Nam, Socialist Republic of Vietnam) and MTDTGPMNVN (Mặt trận Dân tộc Giải phóng miền Nam Việt Nam, Viet Cong). Long initialisms have become widespread in legal contexts in Vietnam, for example TTLT-VKSNDTC-TANDTC.^[85] It is also common for a writer to coin an ad-hoc initialism for repeated use in an article.

Each letter in an initialism corresponds to one morpheme—that is, one syllable. When the first letter of a syllable has a tone mark or other diacritic, the diacritic may be omitted from the initialism, for example ĐNA or ĐNÁ for Đông Nam Á (Southeast Asia) and LMCA or LMCÂ for Liên minh châu Âu (European Union). The letter "Ư" is often replaced by "W" in initialisms to avoid confusion with "U", for example UBTWMTTQVN or UBTƯMTTQVN for Ủy ban Trung ương Mặt trận Tổ quốc Việt Nam (Central Committee of the Vietnamese Fatherland Front).

Initialisms are purely a written convenience, being pronounced the same way as their expansions. As the names of many Vietnamese letters are disyllabic, it would be less convenient to pronounce an initialism by its individual letters. Acronyms pronounced as words are rare in Vietnamese, occurring when an acronym itself is borrowed from another language. Examples include SIĐA (pronounced [s̪i˧ ˀɗaː˧]), a respelling of the French acronym SIDA (AIDS); VOA (pronounced [vwaː˧]), a literal reading of the English initialism for Voice of America; and NASA (pronounced [naː˧ zaː˧]), borrowed directly from the English acronym.

As in Chinese, many compound words can be shortened to the first syllable when forming a longer word. For example, the term Việt Cộng is derived from the first syllables of "Việt Nam" (Vietnam) and "Cộng sản" (communist). This mechanism is limited to Sino-Vietnamese vocabulary. Unlike with Chinese, such clipped compounds are considered to be portmanteau words or blend words rather than acronyms or initialisms, because the Vietnamese alphabet still requires each component word to be written as more than one character.

In languages where nouns are declined, various methods are used. An example is Finnish, where a colon is used to separate inflection from the letters:

The process above is similar to how, in English, hyphens are used for clarity when prefixes are added to acronyms, thus pre-NATO policy (rather than preNATO).

In languages such as Scottish Gaelic and Irish, where lenition (initial consonant mutation) is commonplace, acronyms must also be modified in situations where case and context dictate it. In the case of Scottish Gaelic, a lower case "h" is often added after the initial consonant; for example, BBC Scotland in the genitive case would be written as BhBC Alba, with the acronym pronounced VBC. Likewise, the Gaelic acronym for "television" (gd: telebhisean) is TBh, pronounced TV, as in English.