Head of Hogwarts?
I believe the answer is:
loo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">head of hogwarts?</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for loo that I've seen before include "Rest room" , "A colloquial toilet" , "In which one goes" , "The little room - card game" , "Little boys' room" .)