Catholic inclination to confess, as purification (9)
I believe the answer is:
cleansing
'purification' is the definition.
(thesaurus)
'catholic inclination to confess' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'inclination' becomes 'lean' ('lean' can be a synonym of 'inclination').
'to confess' becomes 'sing' (I've seen this before).
'c'+'lean'+'sing'='CLEANSING'
'as' acts as a link.
(Other definitions for cleansing that I've seen before include "Nice slang for making thoroughly free from dirt (9)" , "Purging" .)