So let it be (4)
I believe the answer is:
amen
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">so let it be</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for amen that I've seen before include "Prayerful last word" , "Response to prayer" , "Put name to end of payer" , "as agreed!" , "Final word in prayer" .)