Large strong box (5)
I believe the answer is:
chest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large strong box</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 chest that I've seen before include "Large, sturdy box with a lid" , "Bust" , "Box or trunk" , "Treasure (or heart) container" , "Large strong box for storage" .)