From Greek 'keration' (carob seed) via Arabic — ancient gem traders used carob seeds as balance weights for diamonds.
A unit of weight for precious stones equal to 200 milligrams; also (as karat), a measure of the purity of gold.
From French 'carat,' from Italian 'carato,' from Arabic 'qīrāṭ' (قيراط), meaning a unit of weight, itself borrowed from Greek 'kerátion' (κεράτιον), meaning 'carob seed' (literally 'little horn,' diminutive of 'kéras,' horn, from the horn-shaped carob pod). Carob seeds were used as balance weights by ancient gem traders because they were believed to be remarkably uniform in weight -- each seed supposedly weighing exactly one carat. Modern research has shown this uniformity was largely