Theia or Rhea (5)
I believe the answer is:
titan
'theia or rhea' is the definition.
(I know that Theia is a Titan)
This is all the clue.
(Other definitions for titan that I've seen before include "Person of heroic stature" , "One of the first pantheon of Greek deities" , "Very strong or important person" , "Giant god of Gr. myth" , "Atlas, say" .)