(1):

(n.) That which is asserted; an assertion; a positive statement; an averment; as, an affirmation, by the vender, of title to property sold, or of its quality.

(2):

(n.) A solemn declaration made under the penalties of perjury, by persons who conscientiously decline taking an oath, which declaration is in law equivalent to an oath.

(3):

(n.) Confirmation of anything established; ratification; as, the affirmation of a law.

(4):

(n.) The act of affirming or asserting as true; assertion; - opposed to negation or denial.