The Collaborative International Dictionary of English v.0.48:

Rationalization \Ra`tion*al*i*za"tion\
   (r[a^]sh`[u^]n*al*[i^]*z[=a]"sh[u^]n), n.
   The act or process of rationalizing.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rationalization
    n 1: the cognitive process of making something seem consistent
         with or based on reason [syn: rationalization,
         rationalisation]
    2: (psychiatry) a defense mechanism by which your true
       motivation is concealed by explaining your actions and
       feelings in a way that is not threatening [syn:
       rationalization, rationalisation]
    3: (mathematics) the simplification of an expression or equation
       by eliminating radicals without changing the value of the
       expression or the roots of the equation [syn:
       rationalization, rationalisation]
    4: the organization of a business according to scientific
       principles of management in order to increase efficiency
       [syn: rationalization, rationalisation]
    5: systematic organization; the act of organizing something
       according to a system or a rationale [syn: systematization,
       systematisation, rationalization, rationalisation]

Moby Thesaurus II by Grady Ward, 1.0:

165 Moby Thesaurus words for "rationalization":
   account, adjustment, alienation, apparent soundness, approach,
   arrangement, attack, autism, autistic thinking,
   avoidance mechanism, blame-shifting, blueprint, blueprinting,
   calculation, casuistry, charting, circularity, clearance, clearing,
   codification, compensation, conception, contrivance, coordination,
   decompensation, deduction, deductive reasoning, defense mechanism,
   demonstration, dereism, dereistic thinking, design,
   destigmatization, destigmatizing, device, discourse,
   discourse of reason, discursive reason, disingenuousness,
   displacement, disposition, dissociation, distortion,
   emotional insulation, enterprise, envisagement, equivocalness,
   equivocation, escape, escape into fantasy, escape mechanism,
   escapism, evasive reasoning, exculpation, explanation,
   fallaciousness, fallacy, fantasizing, fantasy, figuring, flight,
   foresight, forethought, game, graphing, ground plan, guidelines,
   harmonization, idea, induction, inductive reasoning, insincerity,
   intention, isolation, jesuitism, jesuitry, justification, layout,
   lineup, logical thought, long-range plan, mapping, master plan,
   method, methodization, methodology, misapplication, mystification,
   negativism, normalization, obfuscation, obscurantism,
   operations research, ordination, organization, overcompensation,
   oversubtlety, perversion, philosophism, philosophy, plan, planning,
   planning function, plausibility, plausibleness, prearrangement,
   procedure, program, program of action, projection, proof,
   psychotaxis, purgation, purging, ratiocination, rationale,
   rationalism, rationality, rationalizing, reason, reasonableness,
   reasoning, regularization, regulation, rehabilitation,
   reinstatement, resistance, restoration, routinization, schedule,
   schema, schematism, schematization, scheme, scheme of arrangement,
   setup, sociological adjustive reactions, sophism,
   sophistical reasoning, sophistication, sophistry, special pleading,
   speciosity, specious reasoning, speciousness, strategic plan,
   strategy, sublimation, substitution, subtlety, sweet reason,
   system, systematization, tactical plan, tactics, the big picture,
   the picture, vicious circle, vicious reasoning, vindication, way,
   wish-fulfillment fantasy, wishful thinking, withdrawal,
   working plan