One church had to be decorated (4)
I believe the answer is:
iced
'decorated' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'one church had' is the wordplay.
'one' becomes 'i' (Roman numeral).
'church' becomes 'CE' (abbreviation for Church of England).
'had' becomes 'd' (in contractions e.g. 'I'd', 'you'd' etc).
'i'+'ce'+'d'='ICED'
'to be' is the link.
Can you help me to learn more?
(Other definitions for iced that I've seen before include "Made very cold" , "Ultra-cold" , "Kept cool" , "found thus in freezer?" , "hidden under white crystals?" .)