carat

/ˈkɛrət/

Other forms: carats

Precious jewels are measured in carats instead of ounces or grams. If your sister gets a three-carat diamond ring, she's getting a ring that weighs 600mg, which is big enough to be called "a rock."

A variant of carat is karat. The former is usually used with diamonds and is a measure of weight, whereas the latter is usually used for gold and is a measure of purity. One karat is 1/24th of the mass, so 24-karat gold is pure. An 18-karat gold ring is 18/24 (or 3/4) gold and 6/24 (or 1/4) other metals.

Definitions of carat

1. noun

   the unit of measurement for the proportion of gold in an alloy; 18-karat gold is 75% gold; 24-karat gold is pure gold
   synonyms: karat, kt

   type of:

   unit, unit of measurement

   any division of quantity accepted as a standard of measurement or exchange
2. noun

   a unit of weight for precious stones = 200 mg
   type of:

   metric weight unit, weight unit

   a decimal unit of weight based on the gram