WordNet (r) 3.0 (2006):

defense mechanism
    n 1: (psychiatry) an unconscious process that tries to reduce
         the anxiety associated with instinctive desires [syn:
         defense mechanism, defense reaction, defence
         mechanism, defence reaction, defense, defence]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "defense mechanism":
   alienation, autism, autistic thinking, avoidance,
   avoidance mechanism, avoidance reaction, avoiding reaction,
   blame-shifting, block, blocking, circumvention, compensation,
   conversion, decompensation, defence, defense, defense in depth,
   defenses, dereism, dereistic thinking, deterrent capacity,
   displacement, dissociation, dodge, duck, ego defenses, elusion,
   elusiveness, emotional insulation, equivocation, escape,
   escape into fantasy, escape mechanism, escapism, evasion,
   evasive action, evasiveness, fantasizing, fantasy, flight,
   forbearance, forestalling, forestallment, getting around, guard,
   isolation, jink, mental block, negative taxis, negativism,
   neutrality, nonintervention, noninvolvement, overcompensation,
   prevention, projection, protection, psychological defenses,
   psychotaxis, rationalization, refraining, repression, resistance,
   self-defense, self-preservation, self-protection, shunning,
   shunting off, shy, sidestep, sidetracking, slip,
   sociological adjustive reactions, sublimation, substitution,
   suppression, symbolization, the defensive, the runaround, ward,
   wish-fulfillment fantasy, wishful thinking, withdrawal, zigzag