Carat (noun)

1. A unit of weight for precious stones and pearls, equal to 0.2 grams (200 milligrams).
2. A unit of weight for gold equal to 1/24 of a troy ounce (3.75 grams) or 1/5 of a gram.

Origin:

From arabic qirat ("a small weight, a seed"), from greek κεράτιον (kerátion, "fruit of the carob tree"), from κέρας (kéras, "horn"), because of the resemblance of the seed to a small horn.

Examples:

1. The diamond ring was 2 carats, making it quite valuable.
2. The gold necklace was 18 carats, meaning it was 75% pure gold.
3. The necklace was set with a 1 carat sapphire in the center.
4. The carat weight of a diamond is a key factor in determining its value.
5. The price of gold is determined by its caratage (purity) and weight.