Stiffener offered by celebrity before church (6)
I believe the answer is:
starch
'stiffener' is the definition.
(starch is used to make fabric stiff)
'celebrity before church' is the wordplay.
'celebrity' becomes 'star' (I've seen this in another clue).
'before' means one lot of letters go next to another.
'church' becomes 'ch' (common abbreviation).
'star'+'ch'='STARCH'
'offered by' acts as a link.
(Other definitions for starch that I've seen before include "Potato, rice constituent; a stiffener" , "Formal quality" , "Charts (anag) - formality" , "Carbohydrate found in potatoes, wheat etc." , "Stiffness; carbohydrate" .)