Large, densely-packed crowd (6)
I believe the answer is:
throng
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large densely-packed crowd</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 throng that I've seen before include "Multitude" , "Pack" , "Troop" , "Dense crowd" , "Large numbers" .)