bull-horn n.

"male of a bovine animal," c. 1200, bule, from Old Norse boli "bull, male of the domestic bovine," perhaps also from an Old English *bula, both from Proto-Germanic *bullon- (source also of Middle Dutch bulle, Dutch bul, German Bulle), perhaps from a Germanic verbal stem meaning "to roar," which survives in some German dialects and perhaps in the first element of boulder (q.v.). The other possibility [Watkins] is that the Germanic word is from PIE root *bhel- (2) "to blow, swell."

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.). Stock market sense "one who seeks to cause a rise in the price of a stock" is from 1714 (compare bear (n.)). The meaning "policeman" is attested by 1859.

Bull-necked is from 1640s. Figurative phrase take the bull by the horns "boldly face or grapple with some danger or difficulty" is recorded by 1711 (Swift). To be a bull in a china shop, figurative of careless and inappropriately destructive use of force, is attested from 1812 and was the title of a popular humorous song in 1820s England.

Old English horn "horn of an animal; projection, pinnacle," also "wind instrument" (originally one made from animal horns), from Proto-Germanic *hurni- (source also of German Horn, Dutch horen, Old Frisian horn, Gothic haurn), from PIE root *ker- (1) "horn; head."

Late 14c. as "one of the tips of the crescent moon." The name was retained for a of musical instruments that developed from the hunting horn; the French horn is the true representative of the class. Of dilemmas from 1540s; of automobile warning signals from 1901. Slang meaning "erect penis" is suggested by c. 1600. Jazz slang sense of "trumpet" is by 1921. Meaning "telephone" is by 1945. Figurative senses of Latin cornu included "salient point, chief argument; wing, flank; power, courage, strength." Horn of plenty is from 1580s. To make horns at "hold up the fist with the two exterior fingers extended" as a gesture of insult is from c.1600.

Symbolic of cuckoldry since mid-15c. (the victim was fancied to grow one on his head). The image is widespread in Europe and perhaps as old as ancient Greece. The German linguist Hermann Dunger ('Hörner Aufsetzen' und 'Hahnrei', "Germania" 29, 1884) ascribes it to a custom surviving into 19c., "the old practice of engrafting the spurs of a castrated cock on the root of the excised comb, which caused them to grow like horns" [James Hastings, "Encyclopedia of Religion and Ethics"] but the image could have grown as well from a general gesture of contempt or insult made to wronged husbands, "who have been the subject of popular jest in all ages" [Hastings].