Assembly room (7)
I believe the answer is:
chamber
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">assembly room</span>' is the definition.<br/ ><span class="explanation-format__explanation">(eg a parliamentary chamber)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for chamber that I've seen before include "vault" , "Room for the judge or the bed" , "Room where a judge transacts business" , "Enclosed cavity, part of gun" , "Judicial assembly - room" .)