a waterfall, esp a large one descending steeply or in steps
steep rapids in a river
a downpour or deluge
a clouding of the lens of the eye or its enclosing membrane, obstructing the passage of light
[via Latin from Greek kataraktēs waterfall, portcullis, from katarassein to dash down, from kata- cata- + arassein to strike, dash; (sense 2) from the idea of a barrier coming down in front of the eye]