Cataract

Two clearly different meanings in current English of the word cataract are nevertheless derived etymologically from the same source: from the Greek καταρῥάκτης (catarrhactes) 'down-rushing', καταράσσειν 'to dash down', compound of the prefix κατά- (cata-) 'down' and the verb ἀράσσειν (arassein) or ῤάσσειν (rassein) 'to dash'. (OED 1989 adds "(But some think it a derivative of καταρρηγνύναι to break down.)" The latin catarcta derived from the Greek can mean 'waterfall', 'portcullis', or 'floodgate'.

• Cataract first appeared in English in a translation from the Book of Genesis in the Old Testament which was given in the AV as 'floodgates of heaven' - the 'doors' that kept the rain in the heavens, or opened to provide a downpour or flood. Cataract was also used, from the middle of the sixteenth centurey, to mean 'a waterspout'. Both these meanings are now obsolete, as is 'a portcullis', the sliding grid that 'rushes down' to close a gate. The two current meanings are:
• a substantial waterfall, such as Victoria Falls in Africa and Niagara Falls, in North America, and the oldest called cataracts, in Egypt
  • The six cataracts on the Nile are more like white-water rapids than waterfalls on lesser rivers.
• a medical condition of the eye, in which the lens is clouded and obscured as if by a portcullis. This is a common disorder in age.