The large nutlike seed of a species of Æsculus (Æsculus Hippocastanum), formerly ground, and fed to horses, whence the name. The seed is not considered edible by humans.
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.
Aesculus Whitecedar Chamaecyparis/Thuja