ETYM AS. ears; aers; akin to Old High Germ. ars. German arsch, Dutch aars, Swed. ars, Dan. arts.
(British) The buttocks, or hind part of an animal; the bottom.

ETYM Contr. from bottom in this sense.
1. Vagrant; homeless or unemployed person.
2. A lazy person.

1. The lowest part of anything.
2. The lower side of anything; SYN. underside, undersurface.
3. A cargo ship; SYN. freighter, merchantman, merchant ship.
4. (Baseball) The second half of an inning; while the home team is at bat; SYN. bottom of the inning.

(British slang) Buttocks.

1. The hinder part, posterior, or rump of a person or animal.
2. The back of a book, building, or other object; as opposed to the frontside. back side

Buttocks — often used as a euphemism for ass in idiomatic expressions