See more synonyms for bulb on Thesaurus.com
  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. Symbol: B

Origin of bulb

1560–70; < Latin bulbus < Greek bolbós onion, bulbous plant
Related formsbulbed, adjectivebulb·less, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words for bulb

corn, knob, head, ball, swelling, globe, tumor, protuberance, nub, tuber, bunch, nodule, corm

Examples from the Web for bulb

Contemporary Examples of bulb

Historical Examples of bulb

  • I shall tell you the day when you are to put the bulb in the ground.

    The Black Tulip

    Alexandre Dumas (Pere)

  • Do you mean to say that the bulb has now been in the ground for six days?

    The Black Tulip

    Alexandre Dumas (Pere)

  • Amaryllis Formosissima was in bloom in one week after I planted the bulb.

  • And yet the bulb has not only an honourable character—it has a sort of sacred history.


    Benjamin Taylor

  • The stem is white, squamulose, bulb rugulose, ring superior and entire.

British Dictionary definitions for bulb


  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 leavesCompare 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

Word Origin for 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

Word Origin and History for bulb

1560s, "an onion," from Middle French bulbe (15c.), from Latin bulbus "bulb, bulbous root, onion," from Greek bolbos "plant with round swelling on underground stem." Expanded by 1800 to "swelling in a glass tube" (thermometer bulb, light bulb, etc.).

Online Etymology Dictionary, © 2010 Douglas Harper

bulb in Medicine


  1. A globular or fusiform anatomical structure or enlargement.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

bulb in Science


  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.