Dross (4)
I believe the answer is:
scum
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dross</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for scum that I've seen before include "Impurities that rise to surface of liquid" , "People regarded as worthless, especially criminals" , "Floating dirt on surface" , "Waste matter floating on the surface" , "Floating rubbish" .)