By normal evolution it would be *bittle, but it seems to have been influenced by beetle (n.2). Sometimes applied to soft insects, as black beetle, an old name for the cockroach. As a nickname for the original Volkswagen car, 1946, translating German Käfer.
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."
It forms all or part of: abet; bait (n.) "food used to attract prey;" bait (v.) "to torment, persecute;" bateau; beetle (n.1) "type of insect; bit (n.1) "small piece;" bite; bitter; bitter end; boat; boatswain; -fid; fissile; fission; fissure; giblets; pita; pizza; vent (n.).
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bhinadmi "I cleave," Latin Latin findere "to split, cleave, separate, divide," Old High German bizzan "to bite," Old English bita "a piece bitten off, morsel," Old Norse beita "to hunt with dogs," beita "pasture, food."
Old English wifel "small beetle," from Proto-Germanic *webilaz (source also of Old Saxon wibil, Old High German wibil, German Wiebel "beetle, chafer," Old Norse tordyfill "dung beetle"), cognate with Lithuanian vabalas "beetle," from PIE root *(h)uebh- "to weave," also "to move quickly" (see weave (v.)). The sense gradually narrowed by 15c. to a particular kind of beetle that, in larval or adult stages, bores into plants, often destroying them.