"Purportion" is to make a claim of fact.
"Tom purports that he is the best skier among his friends."
"Tom has made a purportion that he is the best skier among his friends."
Primary synonyms: Claim, Assertion, Insistence, Boast
Vague/secondary synonyms: Apology, Defence.
Antonyms: Discredit, Dismissal, Denial