'Yam' definitions:

Definition of 'yam'

noun

Edible tuber of any of several yams

noun

Any of a number of tropical vines of the genus Dioscorea many having edible tuberous roots [syn: yam, yam plant]

noun

Sweet potato with deep orange flesh that remains moist when baked

noun

Edible tuberous root of various yam plants of the genus Dioscorea grown in the tropics world-wide for food

From: GCIDE

Yam \Yam\ (y[a^]m), 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]