Not so much (4)
I believe the answer is:
less
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not so much</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 less that I've seen before include "Fewer; minus" , "See 12" , "Comparatively little" , "inferior" , "Comparative of 'a little'" .)