Piece of burnt coal (6)
I believe the answer is:
cinder
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">piece of burnt coal</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 cinder that I've seen before include "Exhausted piece of coal" , "Ember" , "Incombustible matter left in the fireplace" , "Piece of burnt-out coal" , "Piece of burnt coal" .)