'within-stream' originates from Modern English, a compound of the preposition 'within' and the noun 'stream'.

'within' derives from Old English 'wiþinnan' (with- + -innan) and 'stream' derives from Old English 'stream' (< Proto-Germanic *straumaz); the hyphenated compound 'within-stream' is a modern English formation used mainly in technical writing.

Initially the component words meant 'inside' ('within') and 'a flowing body of water' ('stream'); as a compound the term has been used in modern usage to denote processes or variability 'inside a single stream' and has retained this specific technical sense.