In Norse mythology, a jötunn or, in the normalised scholarly spelling of Old Norse, j?tunn (; O.N.: Old Norse pronunciation: ['j?ton:]; plural jötnar/j?tnar ['j?tn?z?]) is a type of entity contrasted with gods (Aesir and Vanir) and other non-human figures, such as dwarfs and elves. The entities are themselves ambiguously defined, variously referred to by several other terms, including risi, thurs and troll. The jötnar predominantly dwell in Jötunheimr, however they are sometimes referred to as living in specific geographical locations such as Ægir on Læsø.
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. Some deities, such as Skaði and Gerðr, who are married to Njörðr and Freyr respectively, are themselves described as jötnar. Reference to Skaði's vés in Lokasenna and toponyms such as Skedevi in Sweden suggests that despite being a jötunn, Skaði was worshipped in Old Norse religion. Furthermore, various well-attested deities, such as Odin and Thor, are descendants of the jötnar. This supports the idea that the distinction between gods and jötnar is not clearly defined and they should be seen as different cultures or peoples rather than different types of being. In later Scandinavian folklore, the ambiguity surrounding the entities gives way to negative portrayals. Belief in jötnar also survived in English folklore as ettins.
Old Norse jötunn (also j?tunn) and Old English eoten developed from the Proto-Germanic masculine noun *etunaz. Philologist Vladimir Orel says that semantic connections between *etunaz with Proto-Germanic *etanan ("to eat") makes a relation between the two nouns likely. Proto-Germanic *etanan is reconstructed from Old Norse etall "consuming", Old English etol "voracious, gluttonous", and Old High German filu-ezzal "greedy". Old Norse risi and Old High German riso derive from the Proto-Germanic masculine noun *wrisjon. Orel observes that the Old Saxon adjective wrisi-l?k "enormous" is likely also connected.
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 *þur?nan, which is etymologically connected to Sanskrit turá- "strong, powerful, rich". Several terms are used specifically to refer to female entities that fall into this category, including íviðja (plural íviðjur) and gýgr (plural gýgjar).
Norse myth traces the origin of the jötnar to the proto-being Ymir, a result of growth or sexless reproduction from the entity's body. Ymir is later killed, his body is dismembered to create the world, and the jötnar survive this event by way of sailing through a flood of Ymir's blood. The drowning of the jötnar in a flood is pictured on the hilt of the jötunn sword used by Beowulf to slay Grendel's mother. 
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.
The Icelandic and Norwegian rune poems name the rune þ as thurs and state that thursar cause strife to women.