Real Dictionary

chestnut
colour: Something that is chestnut is dark reddish-brown in colour.
countable noun: A chestnut or chestnut tree is a tall tree with broad leaves.
countable noun: Chestnuts are the reddish-brown nuts that grow on chestnut trees. You can eat chestnuts.

chestnut in American English
reddish-brown
the smooth-shelled, sweet, edible nut of any of a genus (Castanea) of trees of the beech family
noun: any of the several deciduous trees constituting the genus Castanea, of the beech family, having toothed, oblong leaves and bearing edible nuts enclosed in a prickly bur, and including C. dentata ( American chestnut), which has been virtually destroyed by

chestnut in British English
noun: any N temperate fagaceous tree of the genus Castanea, such as C. sativa (sweet or Spanish chestnut), which produce flowers in long catkins and nuts in a prickly bur