Ass may refer to:

• The most common phonological and spelling variation of arse in American English, a word for the anus or for the buttocks
• Ass, from Old English assa, ultimately from Latin asinus, is the older word for donkey.
  • Wild ass may mean the wild donkey, or it may mean its wild relative the onager, also known as a "half ass" -another animal of the horse genus.
  • Figuratively, a buffoon (fool, idiot, clown). The ass (donkey) typified clumsiness and stupidity since ancient times; asshead dates to 1550, to make an ass of oneself to 1590 - this has been conflated with "arse".
• "Asses" is also the (English and Latin) plural of the as, a Roman weight and unit of money.
• Abbreviation of assinatura, Portuguese for "sign(ature)".
• In Old Norse mythology, an Áss is one of the Æsir.
• Ass is the local name of the Italian commune of Asso.
• Ass is the title of a 1973 album by the band Badfinger.

The acronym ASS stands for:

• ASS (gene), a human gene that encodes for the enzyme argininosuccinate synthetase.
• ASS (car), made in France from 1919 to 1920.
• After school special (TV program).
• American Science and Surplus, a seller of surplus and educational goods, many of which are odd, amusing, and/or useful.
• Alness (National Rail code: ASS), a railway station in the United Kingdom ; ; .
• The German generic term for Aspirin (short for Acetylsalicylsäure, acetylsalicylic acid), comparable to the term ASA in some English-speaking countries.
• Advanced SubStation Alpha, a subtitles format.
• Asshole (game), a card game also known as Ass.
• Angle-Side-Side, a faulty proof of congruency of two triangles (also called SSA).
• American Sociological Association, known as the American Sociological Society until 1959.
• Austrian Social Service, an Austrian non-profit organizationoun
• African sleeping sickness.

In Old Norse, the Æsir (singular Ás, feminine Ásynja, feminine plural Ásynjur, Anglo-Saxon Ós, from Proto-Germanic *Ansuz) are the principal gods of the pantheon of Norse mythology. They include many of the major figures, such as Odin, Frigg, Thor, Baldr and Tyr. A second clan of gods, the Vanir, is also mentioned in the Norse mythos: the god Njord and his children, Freyr and Freyja, are the most prominent Vanir gods who join the Æsir as hostages after a war between Æsir and Vanir. The Vanir appear to have mainly been connected with cultivation and fertility and the Æsir were connected with power and war.