Nothing in the diocese is decrepit
I believe the answer is:
senile
'decrepit' is the definition.
(I've seen this in another clue)
'nothing in the diocese' is the wordplay.
'nothing' becomes 'nil' (eg nil is zero in football).
'in the' indicates putting letters inside.
'diocese' becomes 'see' (I've seen this in other clues).
'nil' going inside 'see' is 'SENILE'.
'is' is the link.
(Other definitions for senile that I've seen before include "Relating to old age" , "Mentally weak due to old age" , "Suffering from weaknesses of old age" , "Suffering from ailments of old age" , "Mentally infirm with age" .)