Crab possibly unable to move (6)
I believe the answer is:
nebula
'crab' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'unable to move' is the wordplay.
'to move' indicates anagramming the letters.
'unable' with letters rearranged gives 'NEBULA'.
'possibly' acts as a link.
Can you help me to learn more?
(Other definitions for nebula that I've seen before include "Unable to be like a distant galaxy" , "Misty appearance in the heavens" , "Cloud of gas and dust in outer space" , "Bright patch in sky from distant galaxy (6)." , "Cloudy mass in the heavens" .)