yam

Concise Oxford English Dictionary © 2008 Oxford University Press:
yam/jam/

▶noun

• 1 the edible starchy tuber of a climbing plant, widely distributed in tropical and subtropical countries.

• 2 the plant which yields yams. [Genus Dioscorea: many species.]

• 3 N. Amer. a sweet potato.

– origin C16: from Port. inhame or obs. Sp. iñame, prob. of W. Afr. origin.