In Norse mythology, a jötunn (/ˈjɔːtʊn/;^[1] plural jötnar) is a type of entity contrasted with gods and other figures, such as dwarfs and elves. The entities are themselves ambiguously defined, variously referred to by several other terms, including risi, thurs, and troll.

Although the term giant is sometimes used to gloss the word jötunn and its apparent synonyms in some translations and academic texts, jötnar are not necessarily notably large and may be described as exceedingly beautiful or as alarmingly grotesque.^[2] Some deities, such as Skaði and Gerðr, are themselves described as jötnar, and various well-attested deities, such as Odin, are descendants of the jötnar.

The Norse myth traces the origin of the jötnar to the proto-being Ymir, a result of growth or asexual reproduction from the entity's body. Ymir is later killed, his body dismembered to create the world, and the jötnar survive this event by way of sailing through a flood of Ymir's blood. The jötnar dwell in Jötunheimr. In later Scandinavian folklore, the ambiguity surrounding the entities gives way to negative portrayals.

Old Norse jötunn (also jǫtunn, see Old Norse orthography) and Old English eoten developed from the Proto-Germanic masculine noun *etunaz.^[3] Philologist Vladimir Orel says that semantic connections between *etunaz with Proto-Germanic *etanan makes a relation between the two nouns likely.^[3] Proto-Germanic *etanan is reconstructed from Old Norse etall 'consuming', Old English etol 'voracious, gluttonous', and Old High German filu-ezzal 'greedy'.^[3] Old Norse risi and Old High German riso derive from the Proto-Germanic masculine noun *wrisjon. Orel observes that the Old Saxon adjective wrisi-līke 'enormous' is likely also connected.^[4]

Old Norse þurs, Old English ðyrs, and Old High German duris 'devil, evil spirit' derive from the Proto-Germanic masculine noun *þur(i)saz, itself derived form Proto-Germanic *þurēnan, which is etymologically connected to Sanskrit turá- 'strong, powerful, rich'.^[5] For discussion regarding Old Norse troll and its development, see troll. Several terms are used specifically to refer to female entities that fall into this category, including íviðja (plural íviðjur) and gýgr (plural gýgjar).

The jötnar are frequently attested throughout the Old Norse record. For example, in a stanza of Völuspá hin skamma (found in the poem Hyndluljóð), a variety of origins are provided: völvas are descended from Viðòlfr, all seers from Vilmeiðr, all charm-workers from Svarthöfði, and all jötnar descend from Ymir.^[6]