Affecting moral superiority to nuncio’s aims for reform (13)
I believe the answer is:
sanctimonious
'affecting moral superiority' is the definition.
(someone sanctimonious acts morally superior)
'to nuncio's aims for reform' is the wordplay.
'for reform' indicates an anagram (I've seen this in other clues).
'to'+'nuncios'+'aims'='tonunciosaims'
'tonunciosaims' is an anagram of 'SANCTIMONIOUS'.
(Other definitions for sanctimonious that I've seen before include "Hypocritically moral" , "Hypocritically holy" , "Hypocritically pious" , "Making show of being morally superior" , "Canting" .)