Source : Webster's Revised Unabridged Dictionary (1913)

Groundnut \Ground"nut`\ (-n[u^]t`), n. (Bot.)
   (a) The fruit of the {Arachis hypog[ae]a} (native country
       uncertain); the peanut; the earthnut.
   (b) A leguminous, twining plant ({Apios tuberosa}), producing
       clusters of dark purple flowers and having a root
       tuberous and pleasant to the taste.
   (c) The dwarf ginseng ({Aralia trifolia}). [U. S.] --Gray.
   (d) A European plant of the genus {Bunium} ({B. flexuosum}),
       having an edible root of a globular shape and sweet,
       aromatic taste; -- called also {earthnut}, {earth
       chestnut}, {hawknut}, and {pignut}. [1913 Webster]

Source : WordNet®

groundnut
     n 1: a North American vine with fragrant blossoms and edible
          tubers; important food crop of Native Americans [syn: {groundnut
          vine}, {Indian potato}, {potato bean}, {wild bean}, {Apios
          americana}, {Apios tuberosa}]
     2: nutlike tuber; important food of Native Americans [syn: {potato
        bean}, {wild bean}]
     3: pod of the peanut vine containing usually 2 nuts or seeds;
        `groundnut' and `monkey nut' are British terms [syn: {peanut},
         {earthnut}, {goober}, {goober pea}, {monkey nut}]