Rubbish, waste (5)
I believe the answer is:
dross
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">rubbish</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">waste</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(dross is a kind of waste)</span><br/ ><br/ ></span>
(Other definitions for dross that I've seen before include "Lees" , "Impurity" , "Waste coal - rubbish" , "Refuse - dregs" , "Something of inferior quality" .)