From Latin 'inimicus' (not-friend) — a negation of 'amicus' (friend). Displaced native Old English 'feond' (now 'fiend').
A person who is actively hostile or opposed to someone or something; an adversary.
From Old French 'enemi' (Modern French 'ennemi'), from Latin 'inimīcus' (unfriendly, hostile), a compound of 'in-' (not) and 'amīcus' (friend). Latin 'amīcus' derives from 'amāre' (to love), of uncertain deeper etymology — possibly from a PIE root *am- or a baby-talk origin similar to 'mama.' The English word thus means, at its Latin core, 'not-friend' or 'un-loving one.' It displaced the native
English has three words for 'enemy' from three different sources: 'enemy' from Latin 'inimīcus' (not-friend), 'foe' from Old English 'fāh' (hostile, outlawed), and 'fiend' from Old English 'fēond' (one who hates) — the last of which was the standard Old English word for 'enemy' before French 'enemy' displaced it after the Norman Conquest.