Real Dictionary

onion
variable noun: An onion is a round vegetable with a brown skin that grows underground. It has many white layers on its inside which have a strong, sharp smell and taste.

onion in American English
a plant (Allium cepa) of the lily family, having an edible bulb with a strong, sharp smell and taste
noun: a plant, Allium cepa, of the amaryllis family, having an edible, succulent, pungent bulb

onion in British English
noun: an alliaceous plant, Allium cepa, having greenish-white flowers: cultivated for its rounded edible bulb

onion in Hospitality
noun: An onion is a round vegetable with a light brown skin. It has many white layers on its inside which have a strong, sharp smell and taste.