buttocks n.

Proto-Indo-European root meaning "to strike."

It forms all or part of: abut; baste (v.3) "beat with a stick, thrash;" battledore; beat; beetle (n.2) "heavy wooden mallet;" botony; boutonniere; butt (n.1) "thick end;" butt (v.) "strike with the head;" buttocks; button; buttress; confute; halibut; rebut; refute; sackbut; turbot.

It is the hypothetical source of/evidence for its existence is provided by: Latin *futare "to beat" (in compounds); Old English beadu "battle," beatan "to beat," bytl "hammer, mallet."

"thick end," c. 1400, butte, which probably is related to Middle Dutch and Dutch bot, Low German butt "blunt, dull," Old Norse bauta, from Proto-Germanic *buttan, from PIE root *bhau- "to strike." Or related somehow to Old English buttuc "end, small piece of land," and Old Norse butr "short," from Proto-Germanic *butaz, which is from the same PIE root. Also probably mixed with Old French bot "extremity, end," which also is from Germanic (compare butt (n.3)). The meaning "remainder of a smoked cigarette" is recorded by 1847.

late 13c., singular of buttocks (q.v.).