c. 1400, "A wind instrument made of wood and provided with six finger holes" [Middle English Compendium], from Old French cornet (14c.) "a small horn," diminutive of corn "a horn," from Latin cornu "horn of an animal," also "a bugle horn," from PIE root *ker- (1) "horn; head."
Modern use in reference to a brass instrument with valves is short for cornet-à-pistons "cornet with pistons" (1836, from French).
The quality of the tone is penetrating and unsympathetic, by no means equal to that of the trumpet, for which it is commonly substituted. [Century Dictionary, 1897]
"firm, transparent anterior part of the eyeball," late 14c., from Medieval Latin cornea tela "horny web or sheath," from Latin cornu (genitive cornus) "horn" (from PIE root *ker- (1) "horn; head"). So called for its consistency. Related: Corneal.
early 13c., from Old French unicorne, from Late Latin unicornus (Vulgate), from noun use of Latin unicornis (adj.) "having one horn," from uni- "one" (from PIE root *oi-no- "one, unique") + cornus "horn" (from PIE root *ker- (1) "horn; head").
The Late Latin word translates Greek monoceros, itself rendering Hebrew re'em (Deuteronomy xxxiii.17 and elsewhere), which probably was a kind of wild ox. According to Pliny, a creature with a horse's body, deer's head, elephant's feet, lion's tail, and one black horn two cubits long projecting from its forehead. Compare German Einhorn, Welsh ungorn, Breton uncorn, Old Church Slavonic ino-rogu. Old English used anhorn as a loan-translation of Latin unicornis.