Vast; of the universe (6)
I believe the answer is:
cosmic
I believe this is a double definition.
'vast' is the first definition.
(I've seen this in another clue)
'of the universe' is the second definition.
(I've seen this before)
(Other definitions for cosmic that I've seen before include "Enormous" , "Great" , "Relating to the universe" , "Large -- universal" , "Huge" .)