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

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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Earthnut \Earth"nut`\, n. (Bot.) A name given to various roots, tubers, or pods grown under or on the ground; as to:
   (a) The esculent tubers of the umbelliferous plants Bunium flexuosum and Carum Bulbocastanum.
   (b) The peanut. See Peanut.

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: Webster's Revised Unabridged Dictionary (1913)