Source : Webster's Revised Unabridged Dictionary (1913)

Yam \Yam\ (y[a^]m), n. [Pg. inhame, probably from some native
   name.] (Bot.)
   A large, esculent, farinaceous tuber of various climbing
   plants of the genus {Dioscorea}; also, the plants themselves.
   Mostly natives of warm climates. The plants have
   netted-veined, petioled leaves, and pods with three broad
   wings. The commonest species is {D. sativa}, but several
   others are cultivated.

   {Chinese yam}, a plant ({Dioscorea Batatas}) with a long and
      slender tuber, hardier than most of the other species.

   {Wild yam}.
   (a) A common plant ({Dioscorea villosa}) of the Eastern
       United States, having a hard and knotty rootstock.
   (b) An orchidaceous plant ({Gastrodia sesamoides}) of
       Australia and Tasmania.

Dioscorea \Di`os*co"re*a\, n. [NL. Named after Dioscorides the
   Greek physician.] (Bot.)
   A genus of plants. See {Yam}.

Source : WordNet®

Dioscorea
     n : yams [syn: {genus Dioscorea}]