ass 2 
(ăs)
(ăs)n. pl. ass·es (ăsĭz)
Vulgar Slang
Vulgar Slang
1.
a. The buttocks.
b. The anus.
2. Sexual intercourse.
adj. or assed (ăst)
Idiom: Used in combination with adjectives as an intensive: I don't want to play your dumb-ass game. That is one crazy-ass idea.
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.]