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

n an immense cloud of gas (mainly hydrogen) and dust in interstellar space

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

n (pathology) a faint cloudy spot on the cornea

Type of:
dapple, fleck, maculation, patch, speckle, spot
a small contrasting part of something

n a medicinal liquid preparation intended for use in an atomizer

Type of:
formulation, preparation
a substance prepared according to a formula

n cloudiness of the urine

Type of:
(medicine) any sensation or change in bodily function that is experienced by a patient and is associated with a particular disease

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