Not no (3)
I believe the answer is:
yes
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not no</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for yes that I've seen before include "Affirmative response" , "Agreed" , "Oui" , "I agree" , "Yea" .)