A bulb is the roundish, tear-shaped part of some plants. If you plant a bulb, a flower will pop up. Bulb is also short for light bulb. Don’t try planting that kind, though, because lamps don't grow on trees.

Garlic, onions, and shallots are all bulbs, and many flowering plants also grow from underground bulbs, like lilies and daffodils. A different type of bulb is a light bulb, which shares the rounded shape of the plant version. The meaning of bulb in the 16th century was simply "onion," from the Greek bolbos, "plant with round swelling on underground stem."

Definitions of bulb
  1. noun
    anything with a round shape resembling a teardrop
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    type of:
    round shape
    a shape that is curved and without sharp angles
  2. noun
    a rounded part of a cylindrical instrument (usually at one end)
    “the bulb of a syringe”
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    type of:
    part, portion
    something less than the whole of a human artifact
  3. noun
    electric lamp consisting of a transparent or translucent glass housing containing a wire filament (usually tungsten) that emits light when heated by electricity
  4. noun
    a modified bud consisting of a thickened globular underground stem serving as a reproductive structure
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    the bulb of an onion plant
    aggregate bulb of the multiplier onion
    bulb of the sea squill, which is sliced, dried, and used as an expectorant
    bulbil, bulblet
    small bulb or bulb-shaped growth arising from the leaf axil or in the place of flowers
    type of:
    stalk, stem
    a slender or elongated structure that supports a plant or fungus or a plant part or plant organ
  5. noun
    a rounded dilation or expansion in a canal or vessel or organ
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    type of:
    anatomical structure, bodily structure, body structure, complex body part, structure
    a particular complex anatomical part of a living thing
  6. noun
    lower or hindmost part of the brain; continuous with spinal cord; (`bulb' is an old term for medulla oblongata)
    synonyms: medulla, medulla oblongata
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    type of:
    neural structure
    a structure that is part of the nervous system
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