Smile contemptuously (5)
I believe the answer is:
sneer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">smile contemptuously</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 sneer that I've seen before include "Contemptuous look" , "Contemptuous or mocking smile" , "Curl one's lip" , "Contemptuous expression" , "Speak contemptuously" .)