Source : Webster's Revised Unabridged Dictionary (1913)

Cataract \Cat"a*ract\, n. [L. cataracta, catarracles, a
   waterfall, Gr. ?, ?, fr. ? to break down; in the passive, to
   fall or rush down (of tumors) to burst; kata` down + ? to
   break.]
   1. A great fall of water over a precipice; a large waterfall.

   2. (Surg.) 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. (Mach.) A kind of hydraulic brake for regulating the
      action of pumping engines and other machines; -- sometimes
      called {dashpot}.

Source : WordNet®

cataract
     n 1: clouding of the natural lens of the eye
     2: a large waterfall; violent rush of water over a precipice