The Collaborative International Dictionary of English v.0.48:

Dioscorea \Di`os*co"re*a\, n. [NL. Named after Dioscorides the
   Greek physician.] (Bot.)
   A genus of plants, the roots of which are eaten as yams.
   See Yam.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Dioscorea
    n 1: yams [syn: Dioscorea, genus Dioscorea]