Stone coffin (11)
I believe the answer is:
sarcophagus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stone coffin</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sarcophagus that I've seen before include "Stone coffin" , "Final box" , "form of coffin" .)