Distant cloud unable to be dispersed (6)
I believe the answer is:
nebula
'distant cloud' is the definition.
(I've seen this in another clue)
'unable to be dispersed' is the wordplay.
'to be dispersed' is an anagram indicator.
'unable' anagrammed gives 'NEBULA'.
(Other definitions for nebula that I've seen before include "A little cloudy" , "Mist of gas or stars in the night sky" , "Cosmic cloud" , "Misty appearance in the heavens" , "Diffuse cloud of particles and gas in space" .)