'keyhole' originates from Middle English, specifically the words 'key' and 'hole', where 'key' meant 'a device for opening a lock' and 'hole' meant 'an opening'.

'keyhole' changed from the Middle English word 'keyhol' and eventually became the modern English word 'keyhole'.

Initially, it meant 'an opening for a key', and this meaning has largely remained the same in modern usage.