Yam (yăm), n. [Pg. inhame, probably from some native name.] 1. (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 Dioscorea sativa, but several others are cultivated.[1913 Webster]
2. (Bot.) Any one of several cultural varieties of the sweet potato. [U. S.][Webster 1913 Suppl.]
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.[1913 Webster]