Holy person with cunning formality (6)
I believe the answer is:
starch
'formality' is the definition.
(I've seen this before)
'holy person with cunning' is the wordplay.
'holy person' becomes 'st' (I've seen this in other clues).
'with' says to put letters next to each other.
'cunning' becomes 'arch' (I've seen this before).
'st'+'arch'='STARCH'
(Other definitions for starch that I've seen before include "Carbohydrate found in potatoes, wheat etc." , "ceremony" , "Carbohydrate found in potatoes, wheat, and rice" , "Stuff that stiffens cloth" , "Setter" .)