Congregation affirmation (4)
I believe the answer is:
amen
'congregation affirmation' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amen that I've seen before include "Prayerful last word" , "Churchgoer's assent?" , "Name for end to prayer" , "Final word in prayer" , "Prayer ending" .)