A bachelor is a man who is socially regarded as able to marry, but has not yet.^[1]

The word is first attested as the 12th-century bacheler, a knight bachelor, a knight too young or poor to gather vassals under his own banner.^[2] The Old French bacheler presumably derives from Provençal bacalar and Italian baccalare,^[2] but the ultimate source of the word is uncertain.^[3][2] The proposed Medieval Latin *baccalaris ("vassal", "field hand") is only attested late enough that it may have derived from the vernacular languages,^[2] rather than from the southern French and northern Spanish Latin^[3] baccalaria.^[4] Alternatively, it has been derived from Latin baculum ("a stick"), in reference to the wooden sticks used by knights in training.^[5][6]

From the 14th century, the term was also used for a junior member of a guild (otherwise known as "yeomen") or university and then for low-level ecclesiastics, as young monks and recently appointed canons.^[7] As an inferior grade of scholarship, it came to refer to one holding a "bachelor's degree". This sense of baccalarius or baccalaureus is first attested at the University of Paris in the 13th century in the system of degrees established under the auspices of Pope Gregory IX as applied to scholars still in statu pupillari. There were two classes of baccalarii: the baccalarii cursores, theological candidates passed for admission to the divinity course, and the baccalarii dispositi, who had completed the course and were entitled to proceed to the higher degrees.^[8]

In the Victorian era, the term eligible bachelor was used in the context of upper class matchmaking, denoting a young man who was not only unmarried and eligible for marriage, but also considered "eligible" in financial and social terms for the prospective bride under discussion. Also in the Victorian era, the term "confirmed bachelor" denoted a man who was resolute to remain unmarried.

By the later 19th century, the term "bachelor" had acquired the general sense of "unmarried man".

The expression bachelor party is recorded 1882. In 1895, a feminine equivalent "bachelor-girl" was coined, replaced in US English by "bachelorette" by the mid-1930s. After World War II, this terminology came to be seen as antiquated and has been mostly replaced by the gender-neutral term "single" (first recorded 1964). In England and Wales, the term "bachelor" remained the official term used for the purpose of marriage registration until 2005, when it was abolished in favor of "single."^[9]

In certain Gulf Arab countries, "bachelor" can refer to men who are single as well as immigrant men married to a spouse residing in their country of origin (due to the high added cost of sponsoring a spouse onsite),^[10] and a colloquial term "executive bachelor" is also used in rental and sharing accommodation advertisements to indicate availability to white-collar bachelors in particular.^[11]

Bachelors have been subject to penal laws in many countries, most notably in Ancient Sparta and Rome.^[3] At Sparta, men unmarried after a certain age were subject to various penalties (Greek: ἀτιμία, atimía): they were forbidden to watch women's gymnastics; during the winter, they were made to march naked through the agora singing a song about their dishonor;^[3] and they were not provided with the traditional respect due to the elderly.^[12] Some Athenian laws were similar.^[13] Bachelors in Rome fell under the Lex Julia of 18 BC and the Lex Papia Poppaea of AD 9: these lay heavy fines on unmarried or childless people while providing certain privileges to those with several children.^[3] In Britain, taxes occasionally fell heavier on bachelors than other persons: examples include 6 & 7 Will. III, the 1785 Tax on Servants, and the 1798 Income Tax.^[3] Over time, some punishments developed into no more than a teasing game. In some parts of Germany, for instance, men who were still unmarried by their 30th birthday were made to sweep the stairs of the town hall until kissed by a "virgin".

Listed chronologically by date of birth.