Yam, a twining shrub of the East and West Indies. There are several species. The yam is allied to smilax and the lily family. The large, fleshy, tuberous roots are full of starch and are much used for food. The original of the cultivated species is supposed to be the winged yam of the South Sea Islands, whose roots reach a length of thirty inches and a weight of twenty-five or even one hundred pounds. The "yam" of the Southern States is a kind of sweet potato. A genuine wild yam is found in the eastern part of North America. The twining stems of the yam climb over thickets and hang out panicles and racemes of pale, greenish-yellow flowers. The leaves are heart-shaped. See SWEET POTATO.