river: [13] Etymologically, the term river denotes the ‘banks’ of a river, rather than the water that flows between them. Its distant ancestor is Latin rīpa ‘bank’. From this was derived the adjective rīpārius (source of English riparian ‘of a riverbank’ [19]), whose feminine form came to be used in Vulgar Latin as a noun, *rīpāria, denoting ‘land by the water’s edge’.
From it evolved Italian riviera ‘bank’ (whence English Riviera [18]) and Old French riviere. This originally meant ‘river bank’, but this subsequently developed to ‘river’, the sense in which English adopted the word. A heavily disguised English relative is arrive, which etymologically denotes ‘come to the shore’. => arrive, riparian, riviera
river (n.)
early 13c., from Anglo-French rivere, Old French riviere "river, riverside, river bank" (12c.), from Vulgar Latin *riparia "riverbank, seashore, river" (source also of Spanish ribera, Italian riviera), noun use of fem. of Latin riparius "of a riverbank" (see riparian). Generalized sense of "a copious flow" of anything is from late 14c. The Old English word was ea "river," cognate with Gothic ahwa, Latin aqua (see aqua-). Romanic cognate words tend to retain the sense "river bank" as the main one, or else the secondary Latin sense "coast of the sea" (compare Riviera).
U.S. slang phrase up the river "in prison" (1891) is originally in reference to Sing Sing prison, which was literally "up the (Hudson) river" from New York City. Phrase down the river "done for, finished" perhaps echoes sense in sell down the river (1851), originally of troublesome slaves, to sell from the Upper South to the harsher cotton plantations of the Deep South.
