__ to; increases
I believe the answer is:
adds
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">to increases</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 adds that I've seen before include "Aggregates or makes further remark" , "Tots up" , "Calculates the sum" , "Puts in; tacks on" , "Sums, totals" .)