Yam - the thick, starch tuber of various tropical vines native to Asia (genus Dioscorea) unrelated to the potato and sweet potato; has an off-white to dark brown skin, flesh that can range from creamy white to deep red and is less sweet that a sweet potato.
Yarrow - an aromatic herb used in flavoring omelets, stews and salads.
Yeast - a microscopic fungus that converts its food (carbohydrates) into carbon dioxide and alcohol through a metabolic process known as fermentation; yeast is necessary for making beer, wine, cheese and some breads.
Yogurt - curdled or cultured milk dish with custard-like consistency used in main dishes, in sauces and in desserts.
Yorkshire Pudding - a popover-like pastry cooked in roast beef drippings, this is one of the great British inventions. When cooked successfully, it puffs as high as a giant popover, and is crusty and savory with the natural gravy of the roast.