英语词源字典 - 在线词源网站

cataract (n.)[cataract 词源字典]: early 15c., "a waterfall, floodgate," from Latin cataracta "waterfall," from Greek katarhaktes "waterfall, broken water; a kind of portcullis," noun use of an adjective compound meaning "swooping, down-rushing," from kata "down" (see cata-). The second element is traced either to arhattein "to strike hard" (in which case the compound is kat-arrhattein), or to rhattein "to dash, break."

Its alternative sense in Latin of "portcullis" probably was passed through French to form the English meaning "eye disease" (early 15c.), on the notion of "obstruction" (to eyesight).[cataract etymology, cataract origin, 英语词源]
sluice (n.): c. 1400, earlier scluse (mid-14c.), a shortening of Old French escluse "sluice, floodgate" (Modern French écluse), from Late Latin exclusa "barrier to shut out water" (in aqua exclusa "water shut out," i.e. separated from the river), from fem. singular of Latin exclusus, past participle of excludere "to shut out" (see exclude).