'mistress' originates from Middle English and Old French, specifically the Old French word 'maistresse' (later 'maistresse'/'maistresse'), which was the feminine counterpart of 'maistre' (master). Ultimately it traces back to Latin 'magistra', the feminine of 'magister' meaning 'teacher' or 'chief'.

'mistress' changed from Old French 'maistresse' into Middle English forms such as 'maistresse' and later developed into the modern English 'mistress'. The word ultimately derives from Latin 'magistra'/'magister' through Old French.

Initially, it meant 'female teacher' or 'female master/authority' (from the Latin root), but over time it also acquired the sense 'a woman kept by a man or a man's extramarital female lover'; both senses survive in modern usage.