carat

noun

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, diminutive suffix). Doublet of quilate and keratin.

1. A metric unit of mass equal to exactly 200 mg, chiefly used for measuring precious stones and pearls.
2. Any of several small units of mass 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. 24-carat gold is pure.”