The Collaborative International Dictionary of English v.0.48:

Self-defense \Self`-de*fense"\, n.
   The act of defending one's own person, property, or
   reputation.
   [1913 Webster]

   In self-defense (Law), in protection of self, -- it being
      permitted in law to a party on whom a grave wrong is
      attempted to resist the wrong, even at the peril of the
      life of the assailiant. --Wharton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

self-defense
    n 1: the act of defending yourself [syn: self-defense, self-
         defence, self-protection]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "self-defense":
   avoidance reaction, defence, defense, defense in depth,
   defense mechanism, defenses, deterrent capacity, ego defenses,
   escape mechanism, guard, negative taxis, protection,
   psychological defenses, resistance, self-preservation,
   self-protection, the defensive, ward