ass

Etymology 1

From Middle English asse, from Old English assa, back-formed from assen (“she-ass”), from Celtic (compare Old Irish asan, Old Cornish asen), from Latin asinus. Replaced Old English esol, from Proto-West Germanic *asil, also a loanword from the same Latin word.

noun

1. Any of several species of horse-like animals, especially Equus asinus, the domesticated of which are used as beasts of burden.
   In this section "animal" means any horse, cattle, ass, mule, sheep, pig, goat or dog. 1972, Parliament of the United Kingdom, “Part I, section 20(3)”, in Road Traffic Act 1972, page 14
2. (slang, mildly vulgar) A stupid person.
   That new kid left the cap off the syrup bottle again! What an ass.
3. (printing, slang, obsolete) A compositor.
   Sometimes by way of joke, and sometimes by way of irritation, compositors are called Asses by the pressmen. 1841, William Savage, Dictionary of the Art of Printing, page 24

Etymology 2

Variant of arse; used chiefly in North America. Ultimately from Middle English ars, ers, from Old English ærs, ears, from Proto-West Germanic *ars, from Proto-Germanic *arsaz (compare Old High German ars (German Arsch), Old Norse ars, Old Frisian ers), from Proto-Indo-European *h₃érsos (compare Ancient Greek ὄρρος (órrhos)). Etymological notes Contrary to the widespread belief of this being a euphemism, it arose as a pronunciation spelling (of the older form arse still used in the UK, Australia, New Zealand, etc.) that shows the assimilation of /ɹ/ before coronal consonants (especially /s/), a phenomenon that has been present in nonstandard speech from the Middle English period onwards; this is distinct from the later phenomenon of non-rhoticity as /ɹ/ was lost before it could modify the preceding vowel. Other instances of this phenomenon (some of which retained both spellings with different meanings) include cuss from curse, gash from garsh, bass (“fish”) from barse, bust from burst, passel from parcel; see Category:English terms with assimilation of historic /ɹ/ for a more extensive list.

adj

1. (vulgar, slang) Of low quality; bad.
   On a recent episode of "The Justin Dunning Podcast," Starkel shared his thoughts on Martell, a former Ohio State quarterback, saying "he's ass my dude" in reference to Starkel. 2019-02-05, Alex Miller, “Former Texas A&M QB Nick Starkel breaks down old Twitter beef with Tate Martell”, in Dallas Morning News
   For some reason, the teenager thought it’d be a good idea to criticize Newton and say he's "ass" and that he’s "about to be poor" because he's a free agent. 2021-02-21, Thomas Carannante, “Patriots: Cam Newton getting disrespected by a teenager is everything that’s wrong with society”, in Fansided
   "You're so ass," Murray says to another player. 2021-10-28, Josh Weinfuss, “What we learned about Arizona Cardinals quarterback Kyler Murray by watching him on Twitch”, in ESPN

noun

1. (vulgar, slang, countable and uncountable) The buttocks.
2. (vulgar, slang, countable and uncountable) The anus.
3. (vulgar, slang, objectifying, uncountable) Sex; a person to have sex with; with vulgar emphasis on their corporeality (their body) over their personhood.
   I'm going to go down to the bar and try to get me some ass.
   Acid, booze, and ass / Needles, guns, and grass 1971, Joni Mitchell (lyrics and music), “Blue”, in Blue
4. (vulgar, slang, uncountable) Used in similes to express something bad or unpleasant.
   I feel like ass today. ― I am feeling very bad today.
   This room smells like ass. ― This room smells very bad.
   What a bunch of ass. ― What a bunch of lies/nonsense/disappointment.
5. (vulgar, slang, metonymically, objectifying, countable) A person; the self; (reflexively) oneself or one's person, chiefly their body. By extension, one's personal safety, or figuratively one's job, prospects, etc.
   Get your lazy ass out of bed!
   We risk our asses out there every day.
   I'ma get medieval on your ass! (idiomatic sense "on you" (compare go crazy on you), not literally and specifically "on your buttocks")