WordNet sense 1 ((psychiatry) an unconscious process that tries to reduce the anxiety associated with instinctive desires):

defence, defense, defense mechanism, defence mechanism, defence reaction, defense reaction

WordNet sense 2 (the federal department responsible for safeguarding national security of the United States; created in 1947):

DoD, Department of Defense, Defense Department, United States Department of Defense

WordNet sense 3 ((sports) the team that is trying to prevent the other team from scoring):

defending team

WordNet sense 4 (the defendant and his legal advisors collectively):

defense lawyers, defense team

WordNet sense 5 (an organization of defenders that provides resistance against attack):

defence force, defense force

WordNet sense 6 (the speech act of answering an attack on your assertions):

refutation

WordNet sense 7 (the justification for some act or belief):

vindication

WordNet sense 8 (a structure used to defend against attack):

defensive structure

WordNet sense 9 (a defendant's answer or plea denying the truth of the charges against him):

demurrer, denial

WordNet sense 10 (military action or resources protecting a country against potential enemies):

defensive measure