Metropolitan old city with prohibition (5)
I believe the answer is:
urban
'metropolitan' is the definition.
(I've seen this in another clue)
'old city with prohibition' is the wordplay.
'old city' becomes 'ur' (ancient city state).
'with' is a charade indicator (letters next to each other).
'prohibition' becomes 'ban' (synonyms).
'ur'+'ban'='URBAN'
(Other definitions for urban that I've seen before include "Town (adj.)" , "Not rural" , "Relating to towns" , "Of towns or cities" , "City - pope" .)