Mount of Greek myth (4)
I believe the answer is:
ossa
'mount of greek myth' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ossa that I've seen before include "Greek mountains" , "Hard things" , "To heap Pelion on -- is to compound difficulties" , "So as to turn to bones" , "mountain in Thessaly" .)