\Car"at\ (k[a^]r"[a^]t), n. [F. carat (cf. It. carato,
OPg. quirate, Pg. & Sp. quilate), Ar. q[imac]r[=a]t bean or
pea shell, a weight of four grains, a carat, fr. Gr.
kera`tion a little horn, the fruit of the carob tree, a
weight, a carat. See {Horn}.]
1. The weight by which precious stones and pearls are
   weighed.
Note: The carat equals three and one fifth grains Troy, and
      is divided into four grains, sometimes called carat
      grains. Diamonds and other precious stones are
      estimated by carats and fractions of carats, and
      pearls, usually, by carat grains. --Tiffany.
2. A twenty-fourth part; -- a term used in estimating the
   proportionate fineness of gold.
Note: A mass of metal is said to be so many carats fine,
      according to the number of twenty-fourths of pure gold
      which it contains; as, 22 carats fine (goldsmith's
      standard) = 22 parts of gold, 1 of copper, and 1 of
      silver.