'down-river' originates from a combination of Old English 'dūn' (down) and Old French 'riviere' (river), where 'dūn' meant 'downward' and Latin 'ripa' (source of 'riviere') meant 'river bank'.

'down-river' developed from the phrase 'down the river' in Middle English; over time the phrase was written as a compound (often hyphenated) and in modern usage it also appears as the single word 'downriver'.

Initially it meant simply 'toward the lower course of a river'; over time the basic spatial meaning has remained but it has also been used more broadly in figurative contexts to mean 'later in a sequence' or 'at a less central/important position'.