cataract
Merriam-Webster's Word of the Day for July 10, 2021 is: cataract \KAT-uh-rakt\ noun 1 : a clouding of the lens of the eye or of its surrounding transparent membrane that obstructs the passage of light 2 a : [waterfall](https://www.merriam-webster.com/dictionary/waterfall); especially : a large one over a precipice b : steep rapids in a river c : [downpour](https://www.merriam-webster.com/dictionary/downpour), [flood](https://www.merriam-webster.com/dictionary/flood) Examples: "At the cataracts of the great rivers Orinoco, Nile, and Congo, the [syenitic](https://www.merriam-webster.com/dictionary/syenitic) rocks are coated by a black substance, appearing as if they had been polished with [plumbago](https://www.merriam-webster.com/dictionary/plumbago)…. In the Orinoco it occurs on the rocks periodically washed by the floods, and in those parts alone where the stream is rapid…. — [Charles Darwin, The Voyage of the Beagle, 1839](https://www.gutenberg.org/files/944/944-h/944-h.htm) "When cataracts form in your eye, proteins break down and form in clumps in the lens of the eye, creating cloudiness that can make vision blurred or obstructed." — [Rachael Zimlich, Healthline, 1 Apr. 2021](https://www.healthline.com/health/eye-health/cataract-surgery-complications) Did you know? Cataract dates to the 14th century and comes from the Latin word cataracta, meaning "[portcullis](https://www.merriam-webster.com/dictionary/portcullis)." The Latin pertains to the ocular cataract, probably because it obstructs one's vision much like the portcullis's heavy iron grating obstructs passage into a fortress or castle. Cataracta has another meaning, however—"waterfall"—and that meaning gave English the water-related meanings that came in later centuries. The connection between the two Latin meanings can be seen in katarassein, the Greek source of cataracta. It means "to dash down," an action we see in both the slamming portcullis and the cascading waterfall.