unicorn

From Middle English unicorne, unikorn, from Anglo-Norman unicorne, Old French unicorne, and their source, Latin ūnicornis, (from ūnus (“one”) +‎ cornū (“horn”)), a calque of Ancient Greek μονόκερως (monókerōs, “having one horn”, (from μόνος (mónos, “one”) +‎ κέρας (kéras, “horn”))). Displaced native Old English ānhorn, itself a calque of the Latin term. First attested in the early 13th c.

Other senses from either rarity (e.g., possessing multiple skills) or by physical resemblance to having a horn (e.g., howitzer). The finance sense was coined by American investor Aileen Lee and first used in a 2013 article.