The Collaborative International Dictionary of English v.0.48:

Chestnut \Chest"nut\, n. [For chesten-nut; OE. chestein,
   chesten, chastein, chestnut, fr. AS. cisten in cistenbe['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. ?, fr. ? 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 vesce)
      of Europe and America. Commonly two or more of the nuts
      grow in a prickly bur.
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   2. The tree itself, or its light, coarse-grained timber, used
      for ornamental work, furniture, etc.
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   3. A bright brown color, like that of the nut.
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   4. The horse chestnut (often so used in England).
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   5. One of the round, or oval, horny plates on the inner sides
      of the legs of the horse, and allied animals.
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   6. An old joke or story. [Slang]
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   Chestnut tree, a tree that bears chestnuts.
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