Unicorn

unicorn, n. 1. from European mythology and medieval bestiaries, a fabulous animal usu. depicted as having the head of a horse, the hind legs of a stag, the tail of a lion, and a single horn in the middle of its head; from Latin unicornis (uni "one" + cornu "horn"). 2. in fantasy milieux, a magical horse with a single straight white horn; often representing virginal virtue. [GJ1]
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Addendum: See dragon, addendum #2. [GJ1]