City versus John (3)
I believe the answer is:
lav
'john' is the definition.
(both can mean a toilet)
'city versus' is the wordplay.
'city' becomes 'LA' (Los Angeles).
'versus' becomes 'v'.
'la'+'v'='LAV'
(Other definitions for lav that I've seen before include "Private place in short" , "Loo" , "toilet" .)