Pronunciation: (self'di-fens', self"-),[key] —n. 1. the act of defending one's person when physically attacked, as by countering blows or overcoming an assailant: the art of self-defense. 2. a claim or plea that the use of force or injuring or killing another was necessary in defending one's own person from physical attack: He shot the man who was trying to stab him and pleaded self-defense at the murder trial. 3. an act or instance of defending or protecting one's own interests, property, ideas, etc., as by argument or strategy. Also,esp. Brit.,self'-de•fence'.