butt 4 
(bŭt)
(bŭt)n.
1. The larger or thicker end of an object: the butt of a rifle.
2.
a. An unburned end, as of a cigarette.
b. Informal A cigarette.
3. A short or broken remnant; a stub.
4. Informal The buttocks; the rear end.
adv.
Slang Very. Used as an intensive: butt ugly; butt expensive.
[Middle English butte, from Old French but, end, of Germanic origin.]