Horse`-chest"nut (?), n. (Bot.) (a) The large nutlike seed of a species of Æsculus (Æ. Hippocastanum), formerly ground, and fed to horses, whence the name. (b) The tree itself, which was brought from Constantinople in the beginning of the sixteenth century, and is now common in the temperate zones of both hemispheres. The native American species are called buckeyes.