"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.
"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.
"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).
"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.