WordNet sense 1 (the act of asserting that something alleged is not true):

disaffirmation

WordNet sense 2 (a defendant's answer or plea denying the truth of the charges against him):

defense, demurrer, defence, defense

WordNet sense 3 (renunciation of your own interests in favor of the interests of others):

abnegation, self-denial, self-abnegation, self-renunciation