Mountain on the Gulf of Salonika (4)
I believe the answer is:
ossa
'mountain on the gulf of salonika' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ossa that I've seen before include "Hard things" , "So as to become a Greek mountain" , "To pile Pelion upon - is to make even greater" , "Technical name for bones" , "So as to turn to bones" .)