The Oxford Thesaurus An A-Z Dictionary of Synonyms - assertion n.

1) statement, declaration, affirmation, contention, asseveration, averment, avowal, pronouncement; Law affidavit, deposition: He made the assertion that he had never seen the defendant before. 2) insistence, proclamation, representation, affirmation, confirmation: The kings exercised their jurisdiction in the assertion of their regal power.