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.

---

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

---

onion More Idioms  

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

---

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.

From MarketWatch ● Aug. 18, 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

Apart from poppy seeds, the product also contains sesame seeds, sea salt, minced garlic and minced onion.

From BBC ● Aug. 12, 2026

Afterward he searched, though without hope, for another bite of something—a forgotten onion, a mouthful of stewed lentils left from Gebu’s meal.

From "The Golden Goblet" by Eloise Jarvis McGraw

The answer, eventually, was: Then I could finish the peppers and onions and make it another way.

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

Same with precut or packaged lettuce, fresh cilantro, fresh basil, raspberries, snow peas and green onions.

From Salon ● Jul. 25, 2026

I like sprucing up my ramen with fresh bok choy, baby corn, spinach and pickled red onions.

From Salon ● Jul. 19, 2026

The soup he’s making smells delicious, a blend with onions, tomatoes, and spices.

From "Beasts of Prey" by Ayana Gray