CATARACT, a waterfall (Gr. KarappaKrfls, a floodgate, or waterfall, something which rushes down). The earliest use in Eng lish is of a floodgate or portcullis, and this survives in the name of a disease of the eye (see EYE, DISEASES OF ; OPHTHALMOLOGY) . The term is also used of a device to regulate the strokes in certain types of steam-engine.