n. 1 a a fabulous animal with a horse's body and a single straight horn. b a heraldic representation of this, with a twisted horn, a deer's feet, a goat's beard, and a lion's tail. c used in old translations of the Old Testament for the Hebrew re'em, a two-horned animal, probably a wild ox. 2 a a pair of horses and a third horse in front. b an equipage with these. 3 (in full unicorn whale or sea-unicorn) the narwhal.
[ ME f. OF unicorne f. L unicornis f. UNI- + cornu horn, transl. Gk monoceros ]