Yang's opposite (3)
I believe the answer is:
yin
'yang's opposite' is the definition.
(I've seen this in another clue)
This is the entire clue.
(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" .)