Vengeful Olympian (4)
I believe the answer is:
hera
'vengeful olympian' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hera that I've seen before include "Greek queen of Olympian gods" , "Sister and wife of 18" , "Greek equivalent of Juno" , "Consort of Zeus" , "Divinity" .)