French city hardened elderly relative from the East (6)
I believe the answer is:
nantes
'french city' is the definition.
(Nantes is a city in France)
'hardened elderly relative from the east' is the wordplay.
'hardened' becomes 'set' (synonyms).
'elderly relative' becomes 'nan' (informal term for grandmother).
'from the east' shows that the letters should be reversed in order (on a map from right to left).
'set'+'nan'='setnan'
'setnan' written backwards gives 'NANTES'.
(Other definitions for nantes that I've seen before include "Site of historic drownings" , "Loire port; an old Edict" , "A major French port" , "French football club" , "French Atlantic port" .)