'overlord' originates from Middle English, specifically the word 'over-lord', where the element 'over-' meant 'above' and 'lord' meant 'master' or 'ruler'.

'overlord' changed from Middle English 'ouer-lord' (or 'over-lord') and eventually became the modern English word 'overlord'.

Initially, it meant 'a lord who is above other lords' (a superior lord); over time it has come to mean more generally 'a person or power that has dominant control' (including oppressive rulers in historical or fictional usages).