Underground store (6)
I believe the answer is:
cellar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">underground store</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 cellar that I've seen before include "Basement store" , "Underground room - stock of bottled wines" , "Room where wine is usually stored" , "Bottom room where wine is often stored" , "wine stocks" .)