Diminish, lessen (8)
I believe the answer is:
decrease
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">diminish</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that diminish can be written as decrease)</span><br/ ><br/ >'<span class="explanation-format__original">lessen</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that lessen can be written as decrease)</span><br/ ><br/ ></span>
(Other definitions for decrease that I've seen before include "Make or become less" , "Reduce, lessen" , "Grow smaller or less" , "Turn down" , "Make smaller or fewer" .)