[ buhlb ]
See synonyms for bulb on Thesaurus.com
  1. Botany.

    • 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.

    • 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.

  1. Electricity.

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

    • an incandescent or fluorescent electric lamp.

  2. Anatomy. any of various small, bulb-shaped structures or protuberances: olfactory bulb; bulb of urethra.

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

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

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

Origin of bulb

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

Other words from bulb

  • bulbed, adjective
  • bulbless, adjective

Words Nearby bulb

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use bulb in a sentence

British Dictionary definitions for bulb


/ (bʌlb) /

  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

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

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

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

Origin of bulb

C16: from Latin bulbus, from Greek bolbos onion

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for bulb


[ 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. Compare corm rhizome runner tuber.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.