Sound upstairs (4)
I believe the answer is:
sane
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sound upstairs</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 sane that I've seen before include "Mentally sound" , "In full possession of mental faculties" , "Right-minded" , "Healthy in mind" , "Reasonable" .)