Stack (4)
I think it could be either:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stack</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pile that I've seen before include "lot of money" , "large amount of money" , "large building" , "Part of reactor" , "Fortune" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stack</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for heap that I've seen before include "Unreliable old car" , "Rough pile" , "pile-up" , "Mound - dilapidated vehicle" , "Mound, stack" .)