Celestial location with Mars shot (12)
I believe the answer is:
astronomical
'celestial' is the definition.
(thesaurus)
'location with mars shot' is the wordplay.
'with' is a charade indicator (letters next to each other).
'shot' indicates anagramming the letters.
'location' after 'mars' is 'marslocation'.
'marslocation' is an anagram of 'ASTRONOMICAL'.
(Other definitions for astronomical that I've seen before include "Of the study of stars" , "Really, really big" , "Extremely large" , "Tremendous" , "Absolutely huge, in a heavenly way" .)