The 51st Psalm (8)
I believe the answer is:
miserere
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">the 51st psalm</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for miserere that I've seen before include "appeal for mercy" , "Psalm seeking mercy" , "Setting of Psalm fifty one" , "Mercy Seat" , "plea for mercy" .)