Much less (3,5)
I believe the answer is:
let alone
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">much less</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 let alone that I've seen before include "Don't bother someone - allow to be solitary" , "Not to mention, never mind" , "Not to mention (thing)" , "Don't touch" , "Not to mention - much less - avoid" .)