nasturtium armoracia

from The Collaborative International Dictionary of English v.0.48

Horse-radish \Horse"-rad`ish\, n. (Bot.)
   A plant of the genus {Nasturtium} ({Nasturtium Armoracia}),
   allied to scurvy grass, having a root of a pungent taste,
   much used, when grated, as a condiment and in medicine.
   --Gray.
   [1913 Webster]

   {Horse-radish tree}. (Bot.) See {Moringa}.
      [1913 Webster]