Unable to disperse large cloud (6)

I believe the answer is:

nebula

I'm a little stuck... Click here to teach me more about this clue!

'cloud' is the definition.
(I know that nebula is a type of cloud)

'unable to disperse large' is the wordplay.
'unable' anagrams to 'NEBULA'.
Though, I am unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for nebula that I've seen before include "Unable (anag)" , "Hazy light; a slight cloudiness" , "Misty appearance in the heavens" , "Unable to be like a distant galaxy" , "Bright patch in sky from distant galaxy (6)." .)

I've seen this clue in The Guardian.

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