Definition of nebula noun from the Oxford Advanced American Dictionary

 

nebula

 noun
noun
NAmE//ˈnɛbyələ//
 
(pl. nebulae
NAmE//ˈnɛbyəli//
 
)
(astronomy)
 
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a mass of dust or gas that can be seen in the night sky, often appearing very bright; a bright area in the night sky caused by a large cloud of stars that are far away
See the Oxford Advanced Learner's Dictionary entry: nebula