Balance of mind (6)
I believe the answer is:
sanity
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">balance of mind</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sanity that I've seen before include "Sound powers of mind" , "Reason, condition of being compos mentis" , "Stay in (anag.)" , "Rationality" , "presence of mind?" .)