WordReference Random House Learner's Dictionary of American English © 2017
bulb /bʌlb/USA pronunciation   n. [countable]
  1. Botanya rounded root or underground stem of a plant, such as the onion or tulip.
  2. any round, enlarged part, esp. at the end of a long object: the bulb of a thermometer.
  3. Electricitythe part of an incandescent lamp made of glass, through which electricity passes, producing light.

WordReference Random House Unabridged Dictionary of American English © 2017
bulb  (bulb),USA pronunciation n. 
  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, esp. at the end of a cylindrical object:the bulb of a thermometer.
  3. 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.
  4. Anatomyany of various small, bulb-shaped structures or protuberances:olfactory bulb; bulb of urethra.
  5. See  medulla oblongata. 
  6. Buildinga rounded thickening at the toe of an angle iron or tee.
  7. Nautical, Naval Termsa cylindrical or spherical prominence at the forefoot of certain vessels.
  8. Photographya shutter setting in which the shutter remains open as long as the shutter release is depressed. Symbol: B
bulbed, adj. 
bulbless, adj. 
  • Greek bolbós onion, bulbous plant
  • Latin bulbus
  • 1560–70


Collins Concise English Dictionary © HarperCollins Publishers::

bulb /bʌlb/ n
  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
  2. a plant, such as a hyacinth or daffodil, that grows from a bulb
  3. See light bulb
Etymology: 16th Century: from Latin bulbus, from Greek bolbos onion



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