also slug-horn, "a short and ill-formed horn of an ox-like animal," 1825, provincial (East Anglia), from slug (n.2) "stunted horn" + horn (n.).
Entries linking to slughorn
slug n.2
"heavy piece of crude metal for firing from a gun, lead bit, lead bullet not regularly formed," 1620s, perhaps a special use of slug (n.1), which at the time would have meant "lazy person or animal," perhaps on some supposed resemblance.
The meaning "token or counterfeit coin" is recorded from 1881; that of "strong drink" is recorded by 1756, perhaps from the slang phrase fire a slug "take a drink," though it also might be related to Irish slog "swallow."
In typography, "a thin blank of type metal" (1871), hence the journalism sense of "title or short guideline at the head of a news story in draft or galleys" (by 1925), short for slug-line, so called because usually it occupies one slug of type. Sometimes by error they get printed, and if the copy-editor's shorthand instruction is "dead head" or "kill widow," it can look bad.
horn n.
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].