Bulb

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.

any round, enlarged part, especially at the end of a cylindrical object:
the bulb of a thermometer.
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.

Anatomy. any of various small, bulb-shaped structures or protuberances:
olfactory bulb; bulb of urethra.
medulla oblongata.
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.
Contemporary Examples

The Wonderful World of Ramps Jeff Gimmel April 25, 2011
Why You Should Give LED Light Bulbs for Christmas. Seriously. Daniel Gross December 3, 2013
Why You Should Give LED Light Bulbs for Christmas. Seriously. Daniel Gross December 3, 2013
The Best Green Idea in Obama’s Climate-Change Speech Daniel Gross June 24, 2013
Why You Should Give LED Light Bulbs for Christmas. Seriously. Daniel Gross December 3, 2013

Historical Examples

The Jupiter Weapon Charles Louis Fontenay
Chatterbox, 1906 Various
Jewel’s Story Book Clara Louise Burnham
Personal Recollections, from Early Life to Old Age, of Mary Somerville Mary Somerville
In-Door Gardening for Every Week in the Year William Keane

noun
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
a plant, such as a hyacinth or daffodil, that grows from a bulb
See light bulb
a rounded part of an instrument such as a syringe or thermometer
(anatomy) a rounded expansion of a cylindrical organ or part, such as the medulla oblongata
Also called bulbous bow. a bulbous protuberance at the forefoot of a ship to reduce turbulence
n.
bulb
(bŭlb)
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.