carat

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. An old weight equal to a scruple, or the twenty-fourth part of an ounce troy.
2. n. A unit of mass formerly used in various countries for weighing gold. It was generally the 24th part of a mark of gold, and was subdivided into 12 grains. It was commonly equal to about 150.5 troy grains.
3. n. Hence A twenty-fourth part: specifically used in expressing the fineness of gold when used as jewelry. Thus, pure gold being considered as 24 carats fine, if two, six, or ten twenty-fourths of alloy (commonly copper or silver) is present, the gold is said to be 22, 18, or 14 carats fine, and so on. The gold used by jewelers is seldom over 18 carats fine, except in wedding-rings, the standard fineness of which is 22 carats. Gold of 18 carats fine is almost invariably used in mounting diamonds, while 14-carat gold is said to be ordinarily used in the United States for gold chains, etc.
4. n. A unit of weight for precious stones, divided by jewelers into 4 grains, called diamond-grains, but equal to about 3⅙ troy grains, 151½ English carats being taken as equal to an ounce troy. In 1877 the weight of the carat was fixed by a syndicate of London, Paris, and Amsterdam jewelers at 205 milligrams, or 151.76 carats to the troy ounce. Under the translated form κεράτιον, or ceratium, siliqua was adopted by Constantine into the system of weights of the empire as of an ounce, equal to 189 milligrams. In Italy it remained as a part of the system of weights, in general with the same relation to the ounce and with nearly the same value. The Arabic qirat was the 24th part of the mithkal, and was subdivided sometimes into 4, sometimes into 3 grains, its value for gems being very nearly 3 grains troy. The Castilian carat, of a Castilian ounce, or 3.164 troy grains, was, like the rest of the Castilian system, adopted from the Arabs. From Spain this has passed to the rest of Europe and to America, with only small modifications, less than unlegalized units commonly undergo under the name of the Amsterdam or diamond carat, which is usually divided into 64ths. Pearls are sold by the diamond-grain and not by the carat, while small baroque pearls, coral, rough garnets, and the inferior kinds of stones are sold by the ounce troy. The subdivisions of the carat are always expressed in fourths, eighths, sixteenths, etc.
5. n. Often abbreviated car. or K.
6. To try or refine (gold).
7. n. An Arabian coin of base silver, current in Mecca, Medina, and Mocha.

Wiktionary

1. n. A unit of weight for precious stones and pearls, equivalent to 200 milligrams.
2. n. Formerly, any of several units of weight, varying from 189 to 212 mg, the weight of a carob seed.
3. n. A measure of the purity of gold, pure gold being 24 carats.

GNU Webster's 1913

1. n. The weight by which precious stones and pearls are weighed.
2. n. A twenty-fourth part; -- a term used in estimating the proportionate fineness of gold.

WordNet 3.0

1. n. the unit of measurement for the proportion of gold in an alloy; 18-karat gold is 75% gold; 24-karat gold is pure gold
2. n. a unit of weight for precious stones = 200 mg