[horse chestnut] n (1597) 1: a large Asian tree (Aesculus hippocastanum of the family Hippocastanaceae, the horse-chestnut family) that has palmate leaves and erect conical clusters of showy flowers and is widely cultivated as an ornamental and shade tree and naturalized as an escape; also: buckeye
2: the large glossy brown seed of a horse chestnut