Cathedral on right bank (4)
I believe the answer is:
rely
'bank' is the definition.
(to bank on is to rely on)
'cathedral on right' is the wordplay.
'cathedral' becomes 'ely' (cathedral city in Cambridgeshire).
'on' is a charade indicator (letters next to each other).
'right' becomes 'r' (common abbreviation).
'ely' after 'r' is 'RELY'.
(Other definitions for rely that I've seen before include "Count" , "Be dependent" , "Be sure" , "Depend, bank" , "Have confidence or faith in" .)