A devout conclusion (4)
I believe the answer is:
amen
'conclusion' is the definition.
(I have seen 'Conclusion of prayer' mean 'amen' so perhaps 'conclusion' could also mean 'amen')
'a devout' is the wordplay.
'devout' becomes 'men' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'men'='AMEN'
Can you help me to learn more?
(Other definitions for amen that I've seen before include "Religiously 11 [THE LASTWORD]" , "Prayerful last word" , "Response to prayer" , "Word of approval" , "statement of affirmation" .)