Simple - pond (4)
I believe the answer is:
mere
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">simple</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that simple can be written as mere)</span><br/ ><br/ >'<span class="explanation-format__original">pond</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that mere is a type of pond)</span><br/ ><br/ ></span>
(Other definitions for mere that I've seen before include "Lake; simple" , "Former lake" , "Pierre's mother identified" , "President Hollande's mother?" , "Without additions or modifications" .)