onion

American  

[uhn-yuhn] / ˈʌn jən /

noun

• onions
  plural

1. a plant, Allium cepa, of the amaryllis family, having an edible, succulent, pungent bulb.

2. any of certain similar plants.

3. the bulb of the onion plant.

4. the flavor or odor of this bulb.

5. Slang. a person.

   He's a tough onion.

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adjective

1. containing or cooked with onions.

   onion soup.

2. of, relating to, or resembling an onion.

idioms

1. know one's onions, to know one's subject or business thoroughly; be capable or proficient.

onion British  

/ ˈʌnjən /

noun

1. an alliaceous plant, Allium cepa, having greenish-white flowers: cultivated for its rounded edible bulb

2. the bulb of this plant, consisting of concentric layers of white succulent leaf bases with a pungent odour and taste

3. any of several related plants similar to A. cepa, such as A. fistulosum (Welsh onion)

4. slang to be fully acquainted with a subject

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onion More Idioms  

1. see know one's stuff (onions).

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Other Word Forms

Derived Forms

• onionlike
  adjective
• oniony
  adjective

Inflected Forms

Nouns

• onions
  plural

Etymology

Origin of onion

1325–75; Middle English onyon < Old French oignon < Latin ūniōn- (stem of ūniō ) a unity, large pearl, onion; see union

Explanation

An onion is a plant that grows as a bulb underground and can be harvested and eaten. Note: onions may be tasty, but they sure can make your breath stink. Onions are bulbs, like tulips or daffodils — most of the plant is hidden in the soil, with roots stretching down and stalks that grow upward and eventually bloom with small flowers. Onions are typically harvested in the fall, and they come in many shapes, sizes, and colors, all of which can be eaten. The Latin root of onion, unionem, was used in colloquial Roman to mean both "a type of onion" and "a pearl."

Example Sentences

See Examples For:

onion onions

“There’s no cash-producing asset under this — it’s just a big derivative onion tied to a nonsensical index,” he wrote.

From MarketWatch ● Aug. 18, 2026

Roughly chop the onion by hand, or pulse it briefly in a food processor until finely chopped but not puréed.

From Salon ● Aug. 16, 2026

Here, grated yellow summer squash and onion spend the better part of an hour over low heat, slowly becoming soft, sweet and jammy.

From Salon ● Aug. 16, 2026

‘Prawned cocktail, coronation chicken, Black Forest gateau, onion soup. Done properly, they’re all delicious. Where’s all that kind of food gone?’

From Slate ● Aug. 15, 2026

Roommates were forever stepping out of showers, and waitresses appeared out of nowhere to deliver the onion rings and breakfast burritos that stained the pages of the manuscripts.

From "Me Talk Pretty One Day" by David Sedaris

Irrigation supports crops including alfalfa, cotton, onions, pecans, and the area's famous Hatch green chiles.

From Science Daily ● Sep. 3, 2026

Peppers and onions tucked with sausage into bread.

From Salon ● Aug. 25, 2026

Staples at taverns across the state, Maid-Rites more closely resemble the sloppy joe of school lunchrooms: the ground-beef sandwiches are served on a soft bun and topped with mustard, pickles and raw onions.

From The Wall Street Journal ● Jul. 28, 2026

Garlic, ginger and green onions — ingredients that will transform a bowl of ramen from simple to restaurant-quality.

From Salon ● Jul. 19, 2026

Shinae was sitting in the corner peeling onions very slowly and yawning.

From "Finding Junie Kim" by Ellen Oh