Cosmic cloud (6)
I believe the answer is:
nebula
'cosmic cloud' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nebula that I've seen before include "Diffuse cloud of particles and gas in space" , "A little cloudy" , "Gas/dust cloud in space" , "Unable (anag)" , "Mass of interstellar gas" .)