To say nothing of (3,2,7)
I believe the answer is:
not to mention
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">to say nothing of</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for not to mention that I've seen before include "To say nothing of" , "Let alone" .)