Emily Dickinson Lexicon

CAR'AT, n. [It. carato; Fr. carat; D. karaat; G. karat; Gr. κερατιον, a little horn, a pod, and the berry of a pod, used for a weight of four grains. From the Greeks it is said the Arabians borrowed their قرط karat, a weight used in Mecca, equal to the twenty-fourth of a denarius, or denier. See Castel, Col. 3448, and Ludolf, 199.]

1. The weight of four grains, used by goldsmiths and jewelers in weighing precious stones and pearls. – Encyc.
2. The weight that expresses the fineness of gold. The whole mass of gold is divided into 24 equal parts, and as many 24th parts as it contains of pure gold, it is called gold of so many carats. Thus gold of twenty-two parts of pure metal, is gold of twenty-two carats. The carat in Great Britain is divided into four grains; among the Germans into twelve parts; and among the French into thirty-two. – Encyc.
3. The value of any thing. [Obs.] – B. Jonson.