Figure of Greek character with medical degree (5)
I believe the answer is:
rhomb
'figure' is the definition.
(geometric figure)
'greek character with medical degree' is the wordplay.
'greek character' becomes 'rho' (letter from the Greek alphabet).
'with' is a charade indicator (letters next to each other).
'medical degree' becomes 'MB' (Bachelor of Medicine).
'rho'+'mb'='RHOMB'
'of' is the link.
(Other definitions for rhomb that I've seen before include "Diamond shape" , "Figure of four equal sides" , "Quadrilateral with four equal sides" , "Figure on plane" , "Lozenge" .)