Positive plaudit with Ibsen novel (12)
I believe the answer is:
indisputable
'positive' is the definition.
(thesaurus)
'plaudit with ibsen novel' is the wordplay.
'with' says to put letters next to each other.
'novel' indicates an anagram (letters in a new or novel order).
'plaudit'+'ibsen'='plauditibsen'
'plauditibsen' anagrammed gives 'INDISPUTABLE'.
(Other definitions for indisputable that I've seen before include "Unable to be denied" , "Not possible to deny" , "Undeniable" , "it's beyond doubt" .)