Moneylender's safe in old city (6)
I believe the answer is:
usurer
'moneylender's' is the definition.
('usurer' can be a synonym of 'moneylender')
'safe in old city' is the wordplay.
'safe' becomes 'sure' (I've seen this before).
'in' means one lot of letters goes inside another.
'old city' becomes 'ur' (ancient city state).
'sure' going inside 'ur' is 'USURER'.
(Other definitions for usurer that I've seen before include "like Shylock" , "One lending money at unreasonable rates" , "Lender at an exorbitant rate" , "Unfair moneylender" , "He takes much interest" .)