A nebula is a massive cloud of gas and dust in outer space. A nebula is sometimes the birthplace of stars, such as the Orion Nebula where new stars — a youthful million years old — are still forming.

Another example of a nebula is the Crab Nebula — the glowing result of a supernova, noted by Chinese astronomers in 1054 CE. It spans about 10 light-years in length. In biology, a nebula may be a cloudy formation in the eye, or a cloudiness of urine. It also refers to a medicinal preparation put in a nebulizer. When you are talking about more than one nebula (which is probably not that often for the average person), say nebulae.

Definitions of nebula
  1. noun
    an immense cloud of gas (mainly hydrogen) and dust in interstellar space
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    diffuse nebula, gaseous nebula
    a cluster of stars within an intricate cloud of gas and dust
    planetary nebula
    a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star
    Hunter, Orion
    a constellation on the equator to the east of Taurus; contains Betelgeuse and Rigel
    type of:
    any collection of particles (e.g., smoke or dust) or gases that is visible
  2. noun
    (pathology) a faint cloudy spot on the cornea
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    type of:
    dapple, fleck, maculation, patch, speckle, spot
    a small contrasting part of something
  3. noun
    a medicinal liquid preparation intended for use in an atomizer
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    type of:
    formulation, preparation
    a substance prepared according to a formula
  4. noun
    cloudiness of the urine
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    type of:
    (medicine) any sensation or change in bodily function that is experienced by a patient and is associated with a particular disease
Word Family

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