Except if (6)
I believe the answer is:
unless
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">except if</span>' is the definition.<br/ ><span class="explanation-format__explanation">('unless' can mean 'except if...')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for unless that I've seen before include "Except on the condition that" , "Conjunction meaning except when" , "Except, save" , "Though" , "Conditional on" .)