Giant of Greek myth (5)
I believe the answer is:
titan
'giant of greek myth' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for titan that I've seen before include "A giant; Saturn moon" , "Hyperion, for example" , "Taint in old Greek god" , "One of the mythological Greek giants who ruled the world" , "Colossus" .)