Pool of still water (4)
I believe the answer is:
pond
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pool of still water</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for pond that I've seen before include "Small area of still water" , "Possible site for weed" , "Small lake" , "Himalayan country" , "Pool of still water" .)