Bank manager's back, see (4)
I believe the answer is:
rely
'bank' is the definition.
(thesaurus)
'manager's back see' is the wordplay.
'back' suggests the final letters.
'see' becomes 'ely' (example where cathedral located in diocese).
The last letter of 'manager' is 'r'.
'r'+'ely'='RELY'
(Other definitions for rely that I've seen before include "Depend confidently (on)" , "Run and see" , "City with cathedral" , "Depend on with confidence" , "Old rally" .)