The alliaceous, or allium, family includes the onion.
allium definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any strong-smelling bulb plant of a genus (Allium) of the lily family, as the onion, garlic, leek, etc.
Origin: Modern Latin ; from Classical Latin garlic
allium definition by American Heritage Dictionary
Any of numerous, usually bulbous plants of the genus Allium in the lily family, having long stalks bearing clusters of variously colored flowers and including many ornamental and food plants, such as onions, leeks, chives, garlic, and shallots.
Origin: Latin, garlic.