butt (n.1) Look up butt at Dictionary.com
"thick end," O.E. buttuc "end, small piece of land," akin to O.N. butr "short." In sense of "human posterior" it is recorded from mid-15c. Meaning "remainder of a smoked cigarette" first recorded 1847.
butt (n.2) Look up butt at Dictionary.com
"barrel," late 14c., from Anglo-Norm. but and O.Fr. bot "barrel, wineskin" (14c., Mod.Fr. botte), from L.L. buttis "cask" (see bottle). Usually a cask holding 108 to 140 gallons, or roughly two hogsheads, but the measure varied greatly.
butt (n.3) Look up butt at Dictionary.com
"target of a joke," 1610s, originally "target for shooting practice" (mid-14c.), from O.Fr. but "aim, goal, end, target (of an arrow, etc.)," 13c., perhaps from butte "mound, knoll," from Frank. *but (cf. O.N. butr "log of wood"), which would connect it with butt (n.1).
butt (v.) Look up butt at Dictionary.com
"hit with the head," c.1200, from Anglo-Norm. buter, from O.Fr. boter "to push, shove, knock; to thrust against," from V.L. *bottare "thrust," or from Frankish (cf. O.N. bauta, Low Ger. boten "to strike, beat"), from P.Gmc. *butan, from PIE base *bhau- "to strike" (see batter (v.)). To butt in "rudely intrude" is Amer.Eng., 1900.