carat

Etymology

From Middle French carat, from Italian carato, from Arabic قِيرَاط (qīrāṭ, “carat, similarly small units such as inches”), from Ancient Greek κεράτιον (kerátion, “hornlet, carob seed”), from κέρας (kéras, “horn”) + -ιον (-ion, “forming diminutives”). Doublet of karat and quilate.

noun

1. A metric unit of weight equal to exactly 200 mg, chiefly used for measuring precious stones and pearls .
2. (historical) Any of several small units of weight used for measuring precious stones and pearls, equivalent to 189–212 mg.
3. A 24-point scale used to measure the purity of gold.
   18-carat gold is 75% gold by mass. 24k gold is 100% pure.