Celebrity against church formality (6)
I believe the answer is:
starch
'formality' is the definition.
(I've seen this before)
'celebrity against church' is the wordplay.
'celebrity' becomes 'star' (I've seen this before).
'against' is a charade indicator (letters next to each other).
'church' becomes 'ch' (common abbreviation).
'star'+'ch'='STARCH'
(Other definitions for starch that I've seen before include "Carbohydrate found in potatoes, wheat, and rice" , "Fabric stiffener" , "Setter" , "Stiffener in the laundry" , "Carbohydrate found in potatoes, wheat etc." .)