Horse-chest·nut, Horse·chest·nut n.
1. Bot. The large nutlike seed of a species of Aesculus (Aesculus Hippocastanum), formerly ground, and fed to horses, whence the name. The seed is not considered edible by humans. [wns=2]
2. Bot. The tree itself (Aesculus hippocastanum), which was brought from Constantinople in the beginning of the sixteenth century, and is now common in the temperate zones of both hemispheres; it has palmate leaves and large clusters of white to red flowers followed by brown shiny inedible seeds. The native American species is also called buckeye and conker. [wns=1]