Middle English; probably akin to Middle English buttok buttock, Low German butt blunt
Noun (2)
Middle English, partly from Middle French but target, of Germanic origin; akin to Old Norse būtr log, Low German butt blunt; partly from Middle French bute goal, target, mound, from but target
Verb (1) and Noun (3)
Middle English, from Anglo-French buter, boter, of Germanic origin; akin to Old High German bōzan to beat — more at beat