Unable to fault a stellar nursery (6)

I believe the answer is:

nebula

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'a stellar nursery' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'unable to fault' is the wordplay.
'to fault' indicates anagramming the letters (a faulty spelling).
'unable' anagrammed gives 'NEBULA'.

Can you help me to learn more?

(Other definitions for nebula that I've seen before include "Mist of gas or stars in the night sky" , "Cloud of gas and dust in outer space" , "Unable to be like a distant galaxy" , "Cloudy mass in the heavens" , "Cosmic cloud" .)

I've seen this clue in the Sydney Morning Herald.

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