The Collaborative International Dictionary of English v.0.48:

Groundnut \Ground"nut`\ (ground"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]

The Collaborative International Dictionary of English v.0.48:

Hypogaeic \Hyp`o*g[ae]"ic\, a. [Pref. hypo- + Gr. gai^a, gh^,
   earth.] (Chem.)
   Pertaining to, or obtained from, the peanut, or earthnut
   (Arachis hypog[ae]a).
   [1913 Webster]

   Hypog[ae]ic acid (Chem.), an acid in the oil of the
      earthnut, in which it exists as a glyceride, and from
      which it is extracted as a white, crystalline substance.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Peanut \Pea"nut\ (p[=e]"n[u^]t), n. (Bot.)
   The fruit of a trailing leguminous plant (Arachis
   hypog[ae]a); also, the plant itself, which is widely
   cultivated for its fruit.
   [1913 Webster]

   Note: The fruit is a hard pod, usually containing two or
         three seeds, sometimes but one, which ripen beneath the
         soil. Called also earthnut, groundnut, and
         goober.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pindal \Pin"dal\, Pindar \Pin"dar\, n. [D. piendel.] (Bot.)
   The peanut (Arachis hypog[ae]a); -- so called in the West
   Indies.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Arachis hypogaea
    n 1: widely cultivated American plant cultivated in tropical and
         warm regions; showy yellow flowers on stalks that bend over
         to the soil so that seed pods ripen underground [syn:
         peanut, peanut vine, Arachis hypogaea]