BUTTOCK
buttock, cheek
(noun) either of the two large fleshy masses of muscular tissue that form the human rump
Source: WordNet® 3.1
Etymology
Noun
buttock (plural buttocks)
(usually, in the plural) Each of the two large fleshy halves of the posterior part of the body between the base of the back, the perineum and the top of the legs.
The convexity of a ship behind, under the stern.
Usage notes
The plural form is usually used in the singular sense for a single person's posterior, often called butt.
It is rarer to refer to only a single buttock, which is then usually specified as left or right.
Synonyms
• asscheek (crude)
• butt-cheek
• arsecheek (crude)
• bum-cheek
• cheek
• ham
• mound
• hurdies (plural only)
• See also buttocks
Source: Wiktionary
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