Lessen, diminish (7)
I believe the answer is:
dwindle
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">lessen</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that dwindle is a kind of lessen)</span><br/ ><br/ >'<span class="explanation-format__original">diminish</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that dwindle is a kind of diminish)</span><br/ ><br/ ></span>
(Other definitions for dwindle that I've seen before include "Lessen; fade out" , "'Die down, grow less (7)'" , "Become gradually less or smaller" , "Get smaller, less" , "Grow less and fade away" .)