Statement made by discordant air's notes (9)
I believe the answer is:
assertion
'statement' is the definition.
(assertion is a kind of statement)
'discordant air's notes' is the wordplay.
'discordant' indicates anagramming the letters.
'airs'+'notes'='airsnotes'
'airsnotes' with letters rearranged gives 'ASSERTION'.
'made by' is the link.
(Other definitions for assertion that I've seen before include "Emphatic declaration" , "Confident declaration" , "Claim" , "Notarises (anag)" , "Confident statement of fact" .)