The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
bhau-
DEFINITION:
To strike. Oldest form *bhe2u-, colored to *bha2u-, contracted to *bhau-. Derivatives include beat, buttock, halibut, button, and refute. 1.beat, from Old English batan, to beat, from Germanic *bautan.2.beetle3; battledore, from Old English btl, hammer, mallet, from Germanic *bautilaz, hammer. 3.baste3, probably from a Scandinavian source akin to Old Norse beysta, to beat, denominative from Germanic *baut-sti-.4.buttock, from Old English diminutive buttuc, end, strip of land, from Germanic *btaz.5a.halibut, from Middle Dutch butte, flatfish; b.turbot, from a Scandinavian source akin to Old Swedish but, flatfish. Both a and b from Germanic *butt-, name for a flatfish. 6.bouton, butt1, button, buttress; abut, rebut, sackbut, from Old French bo(u)ter, to strike, push, from Germanic *buttan.7. Variant zero-grade form *bh- (< *bhu-, metathesized from *bhu-). Suffixed form *bh-t--.a.confute, from Latin cnftre, to check, suppress, restrain (com-, intensive prefix; see kom); b.refute, from Latin reftre, to drive back, rebut (re-, back; see re-). 8. Possibly reduced suffixed form *bhu-tu- (*bhu-). footle; clafouti, from Latin futuere, to have intercourse with (a woman). (Pokorny 1. bhu- 112.)