downstream

The word 'downstream' is a transparent compound formed within English from the native Germanic elements 'down' and 'stream'. 'Down' originates from the Old English 'dūn' (hill), evolving to signify movement from a higher to a lower place. 'Stream' comes from the Proto-Germanic 'straumaz', itself from the Proto-Indo-European root 'sreu-' meaning 'to flow'. Literally meaning 'in the direction of the flow of the stream', its logic is purely directional, based on the gravitational flow of water from higher to lower ground. This concrete geographical meaning was later extended metaphorically in industrial and business contexts to describe stages in a process that occur later, following the initial or core stages.

Structure: down (direction) + stream (flowing water) - down: From Old English 'dūne', short for 'of dūne' meaning 'from the hill'. It functions as an adverb/adjective indicating a lower position or direction. - stream: From Old English 'strēam', meaning a course of flowing water. It functions as the core noun denoting the flowing body of water.