1. any of the several deciduous trees constituting the genus Castanea, such as C. sativa (sweet or Spanish chestnut), which produce flowers in long catkins and nuts in a prickly bur
2. the edible nut of any of these trees
3. the hard wood of any of these trees, used in making furniture, etc.
4. a. a reddish-brown to brown colour
b. ( as adjective ): chestnut hair
5. a horse of a yellow-brown or golden-brown colour
6. a small horny callus on the inner surface of a horse's leg