Swirling, as yin and yang, showing opposition (9)
I believe the answer is:
naysaying
'opposition' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'swirling as yin and yang' is the wordplay.
'swirling' indicates anagramming the letters.
'and' says to put letters next to each other.
'as'+'yin'='asyin'
'asyin' after 'yang' is 'yangasyin'.
'yangasyin' is an anagram of 'NAYSAYING'.
'showing' acts as a link.
Can you help me to learn more?
(Another definition for naysaying that I've seen is " Refutation".)