Balance, due proportion (8)
I believe the answer is:
symmetry
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">balance</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">due proportion</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for symmetry that I've seen before include "Due proportion" , "Balance in appearance" , "Pleasing proportion of the parts of a thing" , "Arrangement of parts in pleasing proportions" , "shapely attribute" .)