How do you spell Cataract

Available Definitions:
1)  n. - A great fall of water over a precipice; a large waterfall.
2)  n. - An opacity of the crystalline lens, or of its capsule, which prevents the passage of the rays of light and impairs or destroys the sight.
3)  n. - A kind of hydraulic brake for regulating the action of pumping engines and other machines; -- sometimes called dashpot.