Source : Webster's Revised Unabridged Dictionary (1913)

Buckwheat \Buck"wheat`\, n. [Buck a beech tree + wheat; akin to
   D. boekweit, G. buchweizen.]
   1. (Bot.) A plant ({Fagopyrum esculentum}) of the Polygonum
      family, the seed of which is used for food.

   2. The triangular seed used, when ground, for griddle cakes,
      etc.

Source : WordNet®

buckwheat
     n 1: or member of genus Fagopyrum; annual Asian plant with
          clusters of small pinkish white flowers and small edible
          triangular seeds which are used whole or ground into
          flour [syn: {Polygonum fagopyrum}, {Fagopyrum esculentum}]
     2: grain ground into flour