Mortal offence (3)
I believe the answer is:
sin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mortal offence</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sin that I've seen before include "Pride, say" , "Breach of morality" , "Misdeed" , "Trespass" , "Fall from grace" .)