the bulb of an onion plant
"She peeled back the dry outer layers to reveal the crisp white bulb of the onion plant."
bulbous plant having hollow leaves cultivated worldwide for its rounded edible bulb
"The farmer harvested a fresh onion from his garden, admiring the crisp texture of its layered bulbs before storing them in the cellar."
an aromatic flavorful vegetable
"The chef chopped fresh onion to add its aromatic flavor to the soup."
A monocotyledonous plant (Allium cepa), allied to garlic, used as vegetable and spice.
"The chef sliced the onion into thin rings to add both flavor and texture to the soup."
In plain English: An onion is a vegetable with layers of papery skin and crisp, slightly pungent flesh that you eat raw or cooked.
"She chopped up an onion to add some flavor to the soup."
Usage: Use this word when referring specifically to the bulb of an Allium cepa plant that is commonly sliced into rings or diced for cooking. It often appears in phrases describing its pungent flavor profile which mellowed after being cooked.
The word onion entered English via Old French, derived from the Latin ūniōnem meaning "onion." It replaced earlier native terms like knelek and ramsons that had described the same vegetable for centuries in Middle English.