Church provided most of item for baptism — material for gown? (7)
I believe the answer is:
'material for gown?' is the definition.
(a gown may be made from chiffon)
'church provided most of item for baptism' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'provided' becomes 'if' (eg 'provided it's sunny' means 'if it's sunny').
'most of' means to remove the last letter.
'item for baptism' becomes 'font' (a baptised baby is dipped into a font).
'font' with its last letter taken away is 'fon'.
(Other definitions for chiffon that I've seen before include "Fine (semi)transparent fabric", "Light silk/nylon fabric", "Fine transparent fabric", "Fine material", "Fine, near-transparent fabric".)