More certain (5)
I believe the answer is:
surer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">more certain</span>' is the definition.<br/ ><span class="explanation-format__explanation">('sure' can be a synonym of 'certain')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for surer that I've seen before include "faster" , "more right?" , "More certain and positive" .)