Source : Webster's Revised Unabridged Dictionary (1913)

Chestnut \Chest"nut\ (ch[e^]s"n[u^]t), n. [For chesten-nut; OE.
   chestein, chesten, chastein, chestnut, fr. AS. cisten in
   cisten-be['a]m chestnut tree, influenced by OF. chastaigne,
   F. ch[^a]taigne, both the AS. and the F. words coming from L.
   castanea a chestnut, Gr. ka`stanon, fr. Ka`stana a city of
   Pontus, where chestnut trees grew in abundance, and whence
   they were introduced into Europe. Cf. {Castanets}.]
   1. (Bot.) The edible nut of a forest tree ({Castanea vesca})
      of Europe and America. Commonly two or more of the nuts
      grow in a prickly bur.

   2. The tree itself, or its light, coarse-grained timber, used
      for ornamental work, furniture, etc.

   3. A bright brown color, like that of the nut.

   4. The horse chestnut (often so used in England).

   5. One of the round, or oval, horny plates on the inner sides
      of the legs of the horse, and allied animals.

   6. An old joke or story. [Slang]

   {Chestnut tree}, a tree that bears chestnuts.

Chestnut \Chest"nut\, a.
   Of the color of a chestnut; of a reddish brown color; as,
   chestnut curls.

Source : WordNet®

chestnut
     n 1: wood of any of various chestnut trees of the genus Castanea
     2: any of several attractive deciduous trees yellow-brown in
        autumn; yield a hard wood and edible nuts in a prickly bur
        [syn: {chestnut tree}]
     3: edible nut of any of various chestnut trees of the genus
        Castanea
     4: a small horny callus on the inner surface of a horse's leg
     5: a dark golden-brown or reddish-brown horse

chestnut
     adj : used of hair; of a golden brown to reddish brown color; "a
           chestnut horse"; "chestnut hair"