Pronunciation: (bulb),[key] —n. 1. Bot. a. 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.
b. a plant growing from such a bud.
2. any round, enlarged part, esp. at the end of a cylindrical object: the bulb of a thermometer. 3. Elect. a. the glass housing, in which a partial vacuum has been established, that contains the filament of an incandescent electric lamp.
b. an incandescent or fluorescent electric lamp.
4. Anat.any of various small, bulb-shaped structures or protuberances: olfactory bulb; bulb of urethra. 5. See medulla oblongata. 6. Building Trades.a rounded thickening at the toe of an angle iron or tee.
7. Naut.a cylindrical or spherical prominence at the forefoot of certain vessels.
8. Photog.a shutter setting in which the shutter remains open as long as the shutter release is depressed. Symbol: B