Desperate old city gentleman (6)
I believe the answer is:
urgent
'desperate' is the definition.
(thesaurus)
'old city gentleman' is the wordplay.
'old city' becomes 'ur' (ancient city state).
'gentleman' becomes 'gent' (gent is a kind of gentleman).
'ur'+'gent'='URGENT'
(Other definitions for urgent that I've seen before include "Requiring immediate action" , "Pressing, compelling" , "Important and in a hurry" , "Pressing, important" , "Calling for immediate attention" .)