a tree, Aesculus hippocastanum, native to the Old World, having digitate leaves and upright clusters of white flowers.
2.
the shiny, brown, nutlike seed of this tree or of other trees of the genus Aesculus.
Origin
1590-1600; translation of Neo-Latincastanea equīna; so named from its use in treating respiratory diseases of horses
British Dictionary definitions for horse chestnut
horse chestnut
noun
1.
any of several trees of the genus Aesculus, esp the Eurasian A. hippocastanum, having palmate leaves, erect clusters of white, pink, or red flowers, and brown shiny inedible nuts enclosed in a spiky bur: family Hippocastanaceae
2.
Also called conker. the nut of this tree
Word Origin
C16: so called from its having been used in the treatment of respiratory disease in horses