Absurdity of Nationalist version of "oneness" (8)
I believe the answer is:
nonsense
'absurdity' is the definition.
(I've seen this before)
'nationalist version of oneness' is the wordplay.
'nationalist' becomes 'n' (abbreviation in politics).
'version of' is an anagram indicator.
'oneness' anagrammed gives 'onsense'.
'n'+'onsense'='NONSENSE'
'of' acts as a link.
(Other definitions for nonsense that I've seen before include "Foolish words or ideas" , "Foolish or meaningless words" , "Baloney" , "folly" , "Rubbish, foolish talk" .)