What does "groundnut" mean?

Groundnut: (a) The fruit of the Arachis hypogæa (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 aud sweet, aromatic taste; -- called also earthnut, earth chestnut, hawknut, and pignut.