'downstream' originates from English, specifically a compound of Old English 'dūn' (later 'down') and Old English 'stream', where 'dūn/down' meant 'from a higher to a lower position' and 'stream' meant 'a current or flowing water'.

'down' (from Old English 'dūn') and 'stream' (Old English 'stream') were compounded in Middle English as 'downstream' to describe the direction or part of a stream; this compound has been used in English since the late Middle English period.

Initially it meant literally 'at or toward the lower part of a stream or river'; over time it also developed figurative uses meaning 'later in a process' or 'in a subsequent stage', which is common in technical and business contexts.