BUTTOCKS
buttocks, nates, arse, butt, backside, bum, buns, can, fundament, hindquarters, hind end, keister, posterior, prat, rear, rear end, rump, stern, seat, tail, tail end, tooshie, tush, bottom, behind, derriere, fanny, ass
(noun) the fleshy part of the human body that you sit on; “he deserves a good kick in the butt”; “are you going to sit on your fanny and do nothing?”
Source: WordNet® 3.1
Noun
buttocks
plural of buttock.
Source: Wiktionary
BUTTOCK
But"tock, n. Etym: [From Butt an end.]
1. The part at the back of the hip, which, in man, forms one of the
rounded protuberances on which he sits; the rump.
2. (Naut.)
Definition: The convexity of a ship behind, under the stern. Mar. Dict.
Source: Webster’s Unabridged Dictionary 1913 Edition