Macrocosm (8)
I believe the answer is:
universe
'macrocosm' is the definition.
(I know that macrocosm can be written as universe)
This is the entire clue.
(Other definitions for universe that I've seen before include "The whole world" , "mind-boggling concept" , "The whole of everything" , "The earth and all the heavenly bodies" , "Edible crustacean" .)