'unlock' originates from Old English, specifically the word 'onlūcan', where 'on-' meant 'opposite' and 'lūcan' meant 'to lock'.

'onlūcan' transformed into the Middle English word 'unlocken', and eventually became the modern English word 'unlock'.

Initially, it meant 'to open or release a lock', and this meaning has largely remained the same in modern usage.