noun
Etymology: so called from the use of its nut to treat respiratory ailments in horses
1.
a. : a large Asian tree of the genus Aesculus ( A.hippocastanum ) that was introduced into Europe in the 16th century and is widely cultivated as an ornamental and shade tree and naturalized as an escape in much of the temperate zone and that has a rough bark, coarse branches, opposite palmately compound leaves, and predominantly white flowers in showy terminal clusters which are followed by large glossy brown seeds enclosed in a coarsely prickly bur ; broadly : any of several trees of the genus Aesculus — see buckeye , tree illustration
b. : the seed of a horse chestnut
2. : a dark grayish brown that is deeper and very slightly redder than average chocolate brown and deeper and very slightly yellower than African brown