O.E. bula "a bull, a steer," or O.N. boli "bull," both from P.Gmc. *bullon- (cf. M.Du. bulle, Ger. Bulle), perhaps from a Gmc. verbal stem meaning "to roar," which survives in some Ger. dialects and perhaps in the first element of boulder
(q.v.). The other possibility is
that it is from PIE *bhln-, from base *bhel- (2) "to blow, swell" (see bole
). An uncastrated male, reared for breeding, as opposed to a bullock or steer. Extended after 1610s to males of other large animals (elephant, alligator, whale, etc.). Bullfrog is from 1738, on resemblance of voice. Stock market sense is from 1714. Bulldyke is from 1926 (see dyke
). Bullheaded "obstinate" is from 1818. Phrase to take the bull by the horns first recorded 1711.