A prayer (6)
I believe the answer is:
orison
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a prayer</span>' is the definition.<br/ ><span class="explanation-format__explanation">('orison' can be a synonym of 'prayer')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for orison that I've seen before include "An archaic or literary prayer" , "Supplication" , "Prayer - O no sir! (anag)" , "O, no, sir, it makes a prayer" .)