noun \ ˈbəlb \
Updated on: 19 Apr 2018

Definition of bulb

1 a : a resting stage of a plant (such 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 (such as a tuber or corm) resembling a bulb in appearance
c : a plant having or developing from a bulb
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 : a rounded or swollen anatomical structure
4 : a camera setting that indicates that the shutter can be opened by pressing on the release and closed by ending the pressure


play \ˈbəlbd\ adjective

Examples of bulb in a Sentence

  1. the bulb of the thermometer

Recent Examples of bulb from the Web

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'bulb.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Illustration of bulb

illustration of bulb

Origin and Etymology of bulb

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

BULB Defined for English Language Learners


Definition of bulb for English Language Learners

  • : 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

BULB Defined for Kids


noun \ ˈbəlb \

Definition of bulb for Students

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 : a plant structure (as a tuber) that is somewhat like a bulb
4 : a rounded object or part
  • the bulb of a thermometer

Medical Dictionary


noun \ ˈbəlb \

medical Definition of bulb

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 : a rounded part: as
a : a rounded enlargement of one end of a part — see bulb of the penis, bulb of the vestibule, end bulb, hair bulb, olfactory bulb
b : medulla oblongata; broadly : the hindbrain exclusive of the cerebellum
c : a thick-walled muscular enlargement of the pharynx of certain nematode worms

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to speak or write verbosely and windily

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