'doomsday' originates from Old English, specifically the word 'dōmes dæg', where 'dōm' meant 'judgment' and 'dæg' meant 'day'.

'dōmes dæg' transformed into the Middle English word 'domesday', and eventually became the modern English word 'doomsday'.

Initially, it meant 'the day of judgment', and this meaning has largely remained the same in modern usage.