Yang's opposite (3)
I believe the answer is:
yin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">yang's opposite</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 yin that I've seen before include "Principle of cold and dark" , "Chinese female passive principle of universe" , "Complement of yang" , "principle accepted in China" , "Comedian Billy Connolly is the big one" .)