On"ion (?), n. [F. ognon, fr. L. unio oneness, unity, a single large pearl, an onion. See One, Union.] Bot.
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 Zool., the grenadier. -- Onion fly Zool. 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.
© Webster 1913.