Definition of "groundnut"

A climbing vine, Apios americana, of eastern North America, having fragrant brownish flowers and small edible tubers.  examples

Any similar plant having underground tubers.  examples

The nutlike tuber of such a plant, especially peanuts.  examples

A plant which bears its nutlike seeds underground, such as a peanut (Arachis hypogaea) or a Bambara groundnut (Vigna subterranea).  examples