Bisect (5)
I believe the answer is:
halve
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bisect</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 halve that I've seen before include "Divide into two equal parts" , "Divide fifty-fifty" , "Cut down substantially" , "cut by fifty percent" , "Reduce by a factor of two" .)