"petty but flashy," 1857, from tin + horn (n.); originally of low-class gamblers, from the tin cans they used for shaking dice.
Entries linking to tinhorn
tin n.
Old English tin, from Proto-Germanic *tinom (source also of Middle Dutch and Dutch tin, Old High German zin, German Zinn, Old Norse tin), of unknown origin, not found outside Germanic.
Other Indo-European languages often have separate words for "tin" as a raw metal and "tin plate;" such as French étain, fer-blanc. Pliny refers to tin as plumbum album "white lead," and for centuries it was regarded as a form of silver debased by lead; hence its figurative use for "mean, petty, worthless." The chemical symbol Sn is from Late Latin stannum (see stannic).
Meaning "container made of tin" is from 1795. Tin-can is from 1770; as naval slang for "destroyer," by 1937. Tin-type in photography is from 1864. Tin ear "lack of musical discernment" is from 1909. Tin Lizzie "early Ford, especially a Model T," first recorded 1915.
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].