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noun \ˈbəlb\

Simple Definition of bulb

  • : a rounded part of some plants that is under the ground and that grows into a new plant during the growing season

  • : a part that has a rounded shape

Source: Merriam-Webster's Learner's Dictionary

Full Definition of bulb

  1. 1 a :  a resting stage of a plant (as the lily, onion, hyacinth, or tulip) that is usually formed underground and consists of a short stem base bearing one or more buds enclosed in overlapping membranous or fleshy leaves b :  a fleshy structure (as a tuber or corm) resembling a bulb in appearance c :  a plant having or developing from a bulb

  2. 2 :  a bulb-shaped part; specifically :  a glass envelope enclosing the light source of an electric lamp or such an envelope together with the light source it encloses

  3. 3 :  a rounded or swollen anatomical structure

  4. 4 :  a camera setting that indicates that the shutter can be opened by pressing on the release and closed by ending the pressure

bulbed play \ˈbəlbd\ adjective

Examples of bulb in a sentence

  1. the bulb of the thermometer

Illustration of bulb

Origin of bulb

Middle English, from Latin bulbus, from Greek bolbos bulbous plant

First Known Use: 15th century

BULB Defined for Kids


noun \ˈbəlb\

Definition of bulb for Students

  1. 1 :  light bulb

  2. 2 :  a dormant stage of a plant that is formed underground and consists of a very short stem with one or more flower buds surrounded by special thick leaves

  3. 3 :  a plant structure (as a tuber) that is somewhat like a bulb

  4. 4 :  a rounded object or part <the bulb of a thermometer>

Medical Dictionary


noun \ˈbəlb\

Medical Definition of bulb

  1. 1:  a rounded dilation or expansion of something cylindrical <the bulb of a thermometer>; especially :  a rounded or pear-shaped enlargement on a small base <the bulb of an eyedropper>

  2. 2:  a rounded part: asa:  a rounded enlargement of one end of a part—see bulb of the penis, bulb of the vestibule, end bulb, hair bulb, olfactory bulbb:  medulla oblongata; broadly :  the hindbrain exclusive of the cerebellumc:  a thick-walled muscular enlargement of the pharynx of certain nematode worms

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