"one who wins a country, subjugates a people, or defeats an adversary," c. 1300, from Anglo-French conquerour, Old French conquereor, from Old French conquerre "conquer, defeat, vanquish," from Vulgar Latin *conquaerere (for Latin conquirere) "to search for, procure by effort, win," from assimilated form of Latin com-, here perhaps an intensive prefix (see com-), + quaerere "to seek, gain" (see query (v.)).
Another early form was conquestor, from the Latin agent noun, conquistor, conquaestor. Fem. form conqueress is attested from c. 1400. William Duke of Normandy was called William the Conqueror from early 12c. in Anglo-Latin (Guillelmus Magus id est conqustor rex Anglorum), by late 14c. in English.