Trust right cathedral city (4)
I believe the answer is:
rely
'trust' is the definition.
(I know that rely is a more specific form of the action trust)
'right cathedral city' is the wordplay.
'right' becomes 'r' (common abbreviation).
'cathedral city' becomes 'ely' (English city with a cathedral).
'r'+'ely'='RELY'
(Other definitions for rely that I've seen before include "Depend confidently (on)" , "Be dependent" , "Depend on with confidence" , "Trust, depend" , "Count" .)