carat Definition

carat
noun

1. A unit of mass, equal to 0.2g, used to measure the mass of gemstones, especially diamonds.
2. A unit used to express the purity of gold in an alloy with another metal (usually copper), equal to the number of parts of gold in 24 parts of the alloy.

Etymology: 16c: French, from Arabic qirat 4-grain weight, from Greek keration carob bean, 3.3-grain weight.