Etymology
1. O.E.
bula "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 is some Ger. dialects and perhaps in the first element of boulder (q.v.). The other possibility is that it is from PIE
*bhel- "to inflate, swell" (the source also of the Gk. word for "whale;" see bole). An uncastrated male, reared for breeding, as opposed to a
bullock or
steer. Extended after 1615 to males of other large animals (elephant, alligator, whale, etc.). Stock market sense is from 1714.
Bulldog is from 1500, perhaps from shape, perhaps originally used for baiting bulls;
bullfrog is from 1738, on resemblance of voice.
Bulldyke is from 1926 (see dyke).
Bull's eye "center of a target" is from 1833.
Bullpen in the baseball sense is first recorded 1915, perhaps from earlier slang meaning "temporary holding cell for prisoners" (1809). Phrase
to take the bull by the horns first recorded 1711.
2. Etymology tree
3. Proto-Indo-European *bʰel-der.
4. Proto-Germanic *bulô
5. Old English bula
6. ▲
7. Proto-Germanic *bulô
8. Old Norse bolibor.
9. Middle English bole
10. English bull
11. From Middle English bole, bul, bule, from a conflation of Old English bula (“bull, steer”) and Old Norse boli, both from Proto-Germanic *bulô (“bull”), from Proto-Indo-European *bʰl̥no-, from *bʰel- (“to blow, swell up”). Cognate with West Frisian bolle, Dutch bul, German Low German Bull, German Bulle, Swedish bulla; also Old Irish ball (“limb”), Latin follis (“bellows, leather bag”), Albanian bolle (“testicles”), Ancient Greek φαλλός (phallós, “penis”). Of sense 11, (a man or boy), derived from the Philadelphia English pronunciation of boy, which is practically a homophone of bull. See: Swedish '
bulla'.