Gas clouds, unable to be dispersed, rose at last (7)
I believe the answer is:
nebulae
'gas clouds' is the definition.
'nebulae' can be an answer for 'clouds' (I've seen this before). I am not certain of the 'gas' bit.
'unable to be dispersed rose at last' is the wordplay.
'to be dispersed' indicates an anagram.
'at last' suggests the final letters.
The last letter of 'rose' is 'e'.
'unable' is an anagram of 'nebula'.
'nebula'+'e'='NEBULAE'
Can you help me to learn more?
(Other definitions for nebulae that I've seen before include "where stars are born" , "Interstellar gas clouds" , "Cloud-like patches in space" , "Gas or dust clouds in space" , "Stardust" .)