The Norse god of thunder (4)
I believe the answer is:
thor
'the norse god of thunder' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for thor that I've seen before include "Germanic deity" , "Scandinavian god of thunder and the weather" , "Imitative artistic work" , "Norse god wielding a hammer" , "Norse god of war" .)