Bucephalus

Proto-Indo-European root meaning "ox, bull, cow," perhaps ultimately imitative of lowing; compare Sumerian gu, Chinese ngu, ngo "ox."

It forms all or part of: beef; Boeotian; Bosphorus; boustrophedon; bovine; bugle; Bucephalus; bucolic; buffalo; bugloss; bulimia; butane; butter; butyl; butyric; cow (n.); cowbell; cowboy; cowlick; cowslip; Euboea; Gurkha; hecatomb; kine.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gaus, Greek bous, Latin bos, Old Irish bo, Latvian guovs, Armenian gaus, Old English cu, German Kuh, Old Norse kyr, Slovak hovado "cow, ox."

In Germanic and Celtic, of females only; in most other languages, of either gender. For "cow" Latin uses bos femina or vacca, a separate word of unknown origin. Other "cow" words sometimes are from roots meaning "horn, horned," such as Lithuanian karvė, Old Church Slavonic krava.

before vowels, cephal-, word-forming element meaning "head, skull, brain," Modern Latin combining form of Greek kephalē "head, uppermost or top part, source," from PIE *ghebh-el- (source also of Tocharian spal "head;" Old High German gebal "skull;" also, via the notion of "front," Gothic gibla, Old Norse gafl "side of a facade").