Grace closing (4)
I believe the answer is:
amen
'grace closing' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for amen that I've seen before include "Religiously 11 [THE LASTWORD]" , "Word at the end of a prayer" , "Word of approval" , "So let it be" , "Extremist" .)