1. unit for measuring the weight of precious stones (equal to 200 milligrams); unit for measuring the quality of gold (also karat). caratcarat (kărăt), n. [f. carat (cf. it. carato, opg. quirate, pg. & sp. quilate), ar. qīrāt bean or pea shell, a weight of four grains, a carat, fr. gr. kera`tion a little horn, the fruit of the carob tree, a weight, a carat. see: horn.]