A sister's on for making new statements (10)

I believe the answer is:

assertions

'statements' is the definition.
(assertion is a kind of statement)

'a sister's on for making new' is the wordplay.
'for making new' indicates anagramming the letters.
'sisters'+'on'='sisterson'
'sisterson' anagrammed gives 'ssertions'.
'a'+'ssertions'='ASSERTIONS'

(Another definition for assertions that I've seen is " Positive statements".)

I've seen this clue in The Times.

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