Divide by two (5)
I believe the answer is:
halve
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">divide by two</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for halve that I've seen before include "split with another" , "make 10 5 say?" , "Reduce by 50%" , "Reduce by a factor of two" , "Divide into two equal parts" .)