Definition of carat

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car·at    (krt) KEY 

NOUN:
Abbr. c or car.

1. A unit of weight for precious stones, equal to 200 milligrams.
2. Variant of karat.

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ETYMOLOGY:
Middle English, from Old French, from Medieval Latin quartus, from Arabic qr, weight of four grains, from Greek kertion, a weight, diminutive of keras, kert-, horn; see ker-¹ in Indo-European roots