Adversary
Middle English: from Old French adversarie, from Latin adversarius ‘opposed, opponent’, from adversus (see adverse).
wiktionary
From Middle English adversarie, from Anglo-Norman aversaire (inWace's Life of Saint Margaret) and Old French aversier, aversaire (French adversaire), from Latin adversārius, from adversus(“turned toward”).
etymonline
adversary (n.)
"unfriendly opponent, enemy" (originally especially of Satan as the enemy of mankind), mid-14c., aduersere, from Anglo-French adverser (13c.), Old French adversarie (12c., Modern French adversaire) "hostile opponent, enemy," or directly from Latin adversarius "an opponent, rival, enemy," noun use of adjective meaning "opposite, hostile, contrary," literally "turned toward one," from adversus "turned against, turned toward, fronting, facing," figuratively "hostile, adverse, unfavorable," past participle of advertere "to turn toward," from ad "to" (see ad-) + vertere "to turn, turn back, be turned; convert, transform, translate; be changed" (see versus). The Latin word is glossed in Old English by wiðerbroca.
