The Collaborative International Dictionary of English v.0.48:

Dissociation \Dis*so`ci*a"tion\ (?; 106), n. [L. dissociatio:
   cf. F. dissociation.]
   1. The act of dissociating or disuniting; a state of
      separation; disunion.
      [1913 Webster]

            It will add infinitely dissociation, distraction,
            and confusion of these confederate republics.
                                                  --Burke.
      [1913 Webster]

   2. (Chem.) The process by which a compound body breaks up
      into simpler constituents; -- said particularly of the
      action of heat on gaseous or volatile substances; as, the
      dissociation of the sulphur molecules; the dissociation of
      ammonium chloride into hydrochloric acid and ammonia.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dissociation
    n 1: the act of removing from association
    2: a state in which some integrated part of a person's life
       becomes separated from the rest of the personality and
       functions independently [syn: dissociation,
       disassociation]
    3: (chemistry) the temporary or reversible process in which a
       molecule or ion is broken down into smaller molecules or ions

Moby Thesaurus II by Grady Ward, 1.0:

104 Moby Thesaurus words for "dissociation":
   alienation, alpha decay, alternating personality, atom-chipping,
   atom-smashing, atomic disintegration, atomic reaction, atomization,
   autism, autistic thinking, avoidance mechanism, beta decay,
   blame-shifting, bombardment, breeding, bullet, catalysis, catalyst,
   chain reaction, cleavage, compensation, decay, decompensation,
   defense mechanism, depersonalization, dereism, dereistic thinking,
   dialysis, disassociation, disconnection, discreteness,
   disintegration series, disjunction, disjuncture, displacement,
   dissociation of personality, double personality, dual personality,
   emotional dissociation, emotional insulation, escape,
   escape into fantasy, escape mechanism, escapism, exchange reaction,
   fantasizing, fantasy, fission, fission reaction, flight,
   gamma decay, hydrolysis, hydrolyst, immateriality, impertinence,
   inapplicability, inappositeness, inconnection, inconsequence,
   independence, ionization, irrelation, irrelevance, isolation,
   mental dissociation, multiple personality, negativism,
   neutron reaction, nonreversible reaction, nuclear fission,
   nucleization, overcompensation, paranoia, paranoid personality,
   personality disorganization, photodisintegration, photolysis,
   projection, proton gun, proton reaction, psychotaxis,
   rationalization, resistance, reversible reaction,
   schizoid personality, schizoidism, schizophrenia, schizothymia,
   separateness, sociological adjustive reactions, split personality,
   splitting, splitting the atom, stimulation, sublimation,
   substitution, target, thermolysis, thermonuclear reaction,
   unconnectedness, unrelatedness, wish-fulfillment fantasy,
   wishful thinking, withdrawal