What does "onion" mean?

Onion: A liliaceous plant of the genus Allium (A.cepa), having a strong-flavored bulb and long hollow leaves; also, its bulbous root, much used as an article of food. The name is often extended to other species of the genus. Onion fish (Zoöl.), the grenadier. -- Onion fly (Zoöl.) a dipterous insect whose larva feeds upon the onion; especially, Anthomyia ceparum and Ortalis flexa. -- Welsh onion. (Bot.) See Cibol. -- Wild onion (Bot.), a name given to several species of the genus Allium.