Weakens (4)
I believe the answer is:
saps
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">weakens</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for saps that I've seen before include "Enervates in spas" , "trenches" , "Vital juices" , "mugs" , "Depletes the the strength of fools" .)