late 14c., "hostile feeling, rivalry, malice; internal conflict," from Old French enemite, variant of enemistié "enmity, hostile act, aversion" (Modern French inimité), from Vulgar Latin *inimicitatem (nominative *inimicitas), from Latin inimicitia "enmity, hostility," usually plural, from inimicus "enemy" (see enemy). Related: Enmities. Amity is basically the same word without the negative prefix.
