'outflow' originates from Old English, specifically the word 'ūtflōwan,' where 'ūt' meant 'out' and 'flōwan' meant 'to flow.'

'ūtflōwan' transformed into the Middle English word 'outflouen,' and eventually became the modern English word 'outflow.'

Initially, it meant 'to flow out,' and this meaning has largely remained the same in modern usage.