'outflow' originates from English, specifically the combination of the prefix 'out' (meaning 'outward') and the noun/verb 'flow' (meaning 'to move in a stream').

'outflow' developed in Middle and Modern English as a compound of 'out' + 'flow' (from Old English elements such as 'ūt'/'ūt(an)' for out and 'flowan' for to flow), eventually becoming the modern compound 'outflow'.

Initially it meant 'the act or process of flowing out' in a physical sense; over time it acquired broader and metaphorical senses such as the movement of people or capital (e.g., financial outflows).