Space cloud (6)
I believe the answer is:
nebula
'space 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 "Unable to find patch in the sky" , "Unable to be like a distant galaxy" , "Misty appearance in the heavens" , "Interstellar gas cloud" , "Mass of interstellar gas" .)