bulb

American  

[buhlb] / bʌlb /

noun

1. Botany.

   1. a usually subterranean and often globular bud having fleshy leaves emergent at the top and a stem reduced to a flat disk, rooting from the underside, as in the onion and lily.

   2. a plant growing from such a bud.

2. any round, enlarged part, especially at the end of a cylindrical object.

   the bulb of a thermometer.

3. Electricity.

   1. the glass housing, in which a partial vacuum has been established, that contains the filament of an incandescent electric lamp.

   2. an incandescent or fluorescent electric lamp.

4. Anatomy. any of various small, bulb-shaped structures or protuberances.

   olfactory bulb; bulb of urethra.

5. medulla oblongata.

6. Building Trades. a rounded thickening at the toe of an angle iron or tee.

7. Nautical. a cylindrical or spherical prominence at the forefoot of certain vessels.

8. Photography. a shutter setting in which the shutter remains open as long as the shutter release is depressed. B

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bulb British  

/ bʌlb /

noun

1. a rounded organ of vegetative reproduction in plants such as the tulip and onion: a flattened stem bearing a central shoot surrounded by fleshy nutritive inner leaves and thin brown outer leaves Compare corm

2. a plant, such as a hyacinth or daffodil, that grows from a bulb

3. See light bulb

4. a rounded part of an instrument such as a syringe or thermometer

5. anatomy a rounded expansion of a cylindrical organ or part, such as the medulla oblongata

6. Also called: bulbous bow.  a bulbous protuberance at the forefoot of a ship to reduce turbulence

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bulb Scientific  

/ bŭlb /

1. A rounded underground storage organ that contains the shoot of a new plant. A bulb consists of a short stem surrounded by fleshy scales (modified leaves) that store nourishment for the new plant. Tulips, lilies, and onions grow from bulbs.

2. Compare corm rhizome runner tuber

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Other Word Forms

• bulbed adjective
• bulbless adjective

Etymology

Origin of bulb

1560–70; < Latin bulbus < Greek bolbós onion, bulbous plant

Explanation

A bulb is the roundish, tear-shaped part of some plants. If you plant a bulb, a flower will pop up. Bulb is also short for light bulb. Don’t try planting that kind, though, because lamps don't grow on trees. Garlic, onions, and shallots are all bulbs, and many flowering plants also grow from underground bulbs, like lilies and daffodils. A different type of bulb is a light bulb, which shares the rounded shape of the plant version. The meaning of bulb in the 16th century was simply "onion," from the Greek bolbos, "plant with round swelling on underground stem."

Example Sentences

Blog comment sections were notoriously dynamic, full of debate and discussion and lots of light bulb moments for writers and readers alike.

From Slate • Mar. 31, 2026

During the Iran hostage crisis, William Daugherty, a newly minted case officer in the CIA’s Directorate of Operations, was kept there, in a 4-foot-wide cell lit 24 hours by a dim, dangling bulb.

From The Wall Street Journal • Mar. 23, 2026

The lightsaber was originally a 1950s camera flash bulb attachment which the production team modified into the piece, according to Propstore's catalogue.

From BBC • Aug. 6, 2025

But it was a light bulb moment with the swing that made the most profound change.

From Los Angeles Times • Jun. 30, 2025

As I move the thin newsprint over the bulb, tiny dots of light shine through the paper.

From "The Bletchley Riddle" by Ruta Sepetys and Steve Sheinkin

Related Words

• corn