cataract

The word comes from Late Middle English cataract, cataracta, or cateracte, meaning 'floodgate of heaven,' via Old French cataracte and Latin cataracta ('floodgate; waterfall'), from Ancient Greek katar(rh)áktēs ('waterfall,' or 'rushing downwards'), itself from katar(rh)ā́ssō ('to pour down; to rush downwards') plus the noun-forming suffix -tēs. That verb likely joins kătă- ('downwards') with arắssō or rhā́ssō ('to dash, strike'), or comes from katarrhēgnúnai ('to break down'). Separately, the eye-clouding sense comes through the same Old French and Latin cataracta, but there in the sense of 'portcullis' — something blocking sight the way a gate blocks a passage — from the same Greek katar(rh)áktēs, which could also mean 'portcullis.'

What began as a word for rushing, downward water — a waterfall or the floodgates of heaven — was borrowed into medicine for the eye condition, on the logic that a clouded lens acts like a portcullis shutting out light. The two meanings, torrent and obstruction, have ridden the same word ever since.

One proposed root behind the 'strike, dash' sense, rhā́ssō, may ultimately trace to Proto-Indo-European *wreh₂ǵʰ- ('to pound, strike'), tying cataract distantly to other words built on the idea of forceful impact.