Evening Trevor, Geoff & Jolan,
Haven't got the crossword but just seen this, I do know that there was once a bible printed with a MISTAKE in it concerning the word 'NOT' being left out of the commandment 'Thou shall (not) commit adultery.
Which would have caused a stir amongst our religious scholars as 'Thou shall commit adultery'
Seeing as the commandments are VOWS, then could it possibly be an Heretical vow if it's asking you to commit Adultery
ADULTERY - this would fit with your 'D' in the second position Trevor
A bit of a stretch maybe, but I've been in contact with Big Dave in the past and he is very proficient and well learned when it comes to clue construction, he can throw in a real tester when he wants.