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.
any round, enlarged part, especially at the end of a cylindrical object: the bulb of a thermometer.
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.
Anatomy. any of various small, bulb-shaped structures or protuberances: olfactory bulb; bulb of urethra.
Building Trades. a rounded thickening at the toe of an angle iron or tee.
Nautical. a cylindrical or spherical prominence at the forefoot of certain vessels.
Photography. a shutter setting in which the shutter remains open as long as the shutter release is depressed. Symbol: B

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

bulbed, adjective
bulbless, adjective
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
bulb (bʌlb)
1.  Compare corm 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
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
[C16: from Latin bulbus, from Greek bolbos onion]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1560s, "an onion," from M.Fr. bulbe, from L. bulbus "bulb, onion," from Gk. 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
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American Heritage
Medical Dictionary

bulb (bŭlb)
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.
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American Heritage
Science Dictionary
bulb  [%PREMIUM_LINK%]     (bŭlb)  Pronunciation Key 
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 © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences for bulbs
Later, magnesium ribbon was used in electrically ignited flash bulbs.
Some lilies form small bulbs, called bulbils in their leaf axils.
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