'onlooker' originates from the combination of 'on' and 'look,' where 'on' meant 'toward' and 'look' meant 'to see.'

'onlooker' evolved from the Middle English word 'onlooken,' which combined 'on' and 'looken,' eventually becoming the modern English word 'onlooker.'

Initially, it meant 'someone who looks on,' and this meaning has largely remained the same in modern usage.