chestnut

1a :  any of a genus (Castanea) of trees or shrubs of the beech family; especially :  an American tree (C. dentata) that was formerly a dominant or codominant member of many deciduous forests of the eastern U.S. but has now been largely eliminated by the chestnut blight and seldom grows beyond the shrub or sapling stageb :  the edible nut of a chestnutc :  the wood of a chestnut

2 :  a grayish to reddish brown

3 :  horse chestnut

4 :  a chestnut-colored animal; specifically :  a horse having a body color of any shade of pure or reddish brown with mane, tail, and points of the same or a lighter shade — compare ²bay 1, ¹sorrel 1

5 :  a callosity on the inner side of the leg of the horse — see horse illustration

6a :  an old joke or storyb :  something (such as a musical piece or a saying) repeated to the point of staleness