Reduce by 50 percent (5)
I believe the answer is:
halve
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">reduce by 50 percent</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 halve that I've seen before include "Divide into two equal parts" , "Reduce by a factor of two" , "Divide into two equal pieces" , "Cut down substantially" , "make 10 5 say?" .)