Celestial hammerer (4)
I believe the answer is:
thor
'celestial hammerer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for thor that I've seen before include "Norse deity" , "Norse god wielding a hammer" , "Scandinavian god of thunder and the weather" , "Norse hammer-wielding god" , "Scandinavian thunder-god" .)