Subtle difference in sister concealing article at church (6)
I believe the answer is:
nuance
'subtle difference' is the definition.
(I've seen this in another clue)
'sister concealing article at church' is the wordplay.
'sister' becomes 'nun' (nuns are referred to as sister).
'concealing' indicates putting letters inside.
'article' becomes 'a' (English indefinite article).
'at' means one lot of letters go next to another.
'church' becomes 'CE' (abbreviation for Church of England).
'nun' enclosing 'a' is 'nuan'.
'nuan'+'ce'='NUANCE'
'in' is the link.
(Other definitions for nuance that I've seen before include "Subtle difference of meaning" , "Subtle distinction or variation" , "Subtlety, nicety" , "A slight shade as of meaning" , "Delicate shade of difference" .)