ass 2 
(
ăs)
n. pl. ass·es (
ăs
ĭz)
Vulgar Slang 1. a. The buttocks.
b. The anus.
2. Sexual intercourse.
adj. or
assed (
ăst)
Used in combination with adjectives as an intensive: I don't want to play your dumb-ass game. That is one crazy-ass idea.
Idiom: have (one's) head up (one's) ass To behave in an ignorant or foolish manner.
[Middle English ars, from Old English ears; see ors- in the Appendix of Indo-European roots.]