car·at / ˈkarət/ • n. 1. a unit of weight for precious stones and pearls, now equivalent to 200 milligrams: a half-carat diamond ring.2. chiefly British spelling of karat.ORIGIN: late Middle English (sense 2): from French, from Italian carato, from Arabic ̣kīrạ̄t (a unit of weight), from Greek keration ‘fruit of the carob’ (also denoting a unit of weight), diminutive of keras ‘horn,’ with reference to the elongated seedpod of the carob.

carat a measure of the purity of gold, pure gold being 24 carats; later also, a unit of weight for precious stones and pearls, now equivalent to 200 milligrams.

Recorded from late Middle English, the word comes via French from Italian carato, from Arabic ḳīrāṭ (a unit of weight), from Greek keration ‘fruit of the carob’ (also denoting a unit of weight), diminutive of keras ‘horn’, with reference to the elongated seed pod of the carob.

carat measure of weight for precious stones; measure of 1/24 used in stating the fineness of gold. XVI. — F. — It. carato — Arab. ḳīrāṭ weight of 4 grains — Gr. kerátion fruit of the carob, f. kéras horn.