Solemn sanction (4)
I believe the answer is:
amen
'solemn sanction' 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 "Prayer ending" , "Name for end to prayer" , "Word of agreement" , "statement of affirmation" , "Name for prayer's end" .)