Deadens (5)
I believe the answer is:
numbs
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">deadens</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for numbs that I've seen before include "Deadens" , "Makes insensitive" .)