Sanctimonious priest’s first evidence of debts (5)
I believe the answer is:
pious
'sanctimonious' is the definition.
(similar in meaning)
'priest's first evidence of debts' is the wordplay.
'priest's first' becomes 'p' (1st letter of 'priest').
'evidence of debts' becomes 'IOUs' (IOU's or I Owe You's).
'p'+'ious'='PIOUS'
(Other definitions for pious that I've seen before include "Devoutly religious" , "Self-righteous" , "Sanctimonious" , "God-fearing" , "Devout" .)