onion

American  

[uhn-yuhn] / ˈʌn yən /

noun

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

• onionlike
  adjective
• oniony
  adjective

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

Tim Cook steps down as Apple’s CEO, RFK Jr. furthers the peptides fad, and The Onion finally gets InfoWars.

From Slate • Apr. 25, 2026

He was tapped by the Onion to help create a streaming network that curates “weird” content from new and established comedians, Heidecker said in an interview.

From The Wall Street Journal • Apr. 24, 2026

The new deal has The Onion paying $81,000 a month to license Infowars.com with an option to renew after six months, according to The New York Times.

From Salon • Apr. 21, 2026

US satirical publication The Onion has proposed a new plan to take over Infowars, the media company run by right-wing conspiracy theorist Alex Jones.

From BBC • Apr. 21, 2026

“My cousin cuts to the bone, as ever. Do you have any more to say to me, Onion Knight, or can we put an end to this mummer’s farce? I grow weary of your face.”

From "A Dance with Dragons" by George R. R. Martin