(1):

(v. t.) To affirm; to declare with assurance, or plainly and strongly; to state positively; to aver; to asseverate.

(2):

(v. t.) To maintain; to defend.

(3):

(v. t.) To maintain or defend, as a cause or a claim, by words or measures; to vindicate a claim or title to; as, to assert our rights and liberties.