The Collaborative International Dictionary of English v.0.48:

Discrimination \Dis*crim`i*na"tion\, n. [L. discriminatio the
   contrasting of opposite thoughts.]
   1. The act of discriminating, distinguishing, or noting and
      marking differences.
      [1913 Webster]

            To make an anxious discrimination between the
            miracle absolute and providential.    --Trench.
      [1913 Webster]

   2. The state of being discriminated, distinguished, or set
      apart. --Sir J. Reynolds.
      [1913 Webster]

   3. (Railroads) The arbitrary imposition of unequal tariffs
      for substantially the same service.
      [1913 Webster]

            A difference in rates, not based upon any
            corresponding difference in cost, constitutes a case
            of discrimination.                    --A. T.
                                                  Hadley.
      [1913 Webster]

   4. The quality of being discriminating; faculty of nicely
      distinguishing; acute discernment; as, to show great
      discrimination in the choice of means.
      [1913 Webster]

   5. That which discriminates; mark of distinction.

   Syn: Discernment; penetration; clearness; acuteness;
        judgment; distinction. See Discernment.
        [1913 Webster]

WordNet (r) 3.0 (2006):

discrimination
    n 1: unfair treatment of a person or group on the basis of
         prejudice [syn: discrimination, favoritism,
         favouritism]
    2: the cognitive process whereby two or more stimuli are
       distinguished [syn: discrimination, secernment]

Moby Thesaurus II by Grady Ward, 1.0:

220 Moby Thesaurus words for "discrimination":
   Atticism, Jim Crow, Jim Crow law, acquired taste, acumen,
   adjudgment, adjudication, aestheticism, alteration, analysis,
   anatomization, anti-Semitism, apartheid,
   appreciation of excellence, appropriateness, arbitrament,
   arbitration, astuteness, atomization, bias, bigotry, black power,
   black supremacy, censoriousness, change, chasteness, chastity,
   chauvinism, choice, choiceness, choosiness, circumspection,
   circumspectness, civilized taste, civilizedness, clarity,
   class consciousness, class distinction, class hatred,
   class prejudice, class war, classicalism, classicism, clearness,
   color bar, color line, comeliness, connoisseurship,
   conscientiousness, consideration, cool judgment, correctness,
   criticalness, cultivated taste, cultivation, culture, daintiness,
   deeming, delicacy, demarcation, desynonymization, differencing,
   differentiation, dignity, directness, discernment, discreetness,
   discretion, discriminatingness, discriminativeness,
   disequalization, disjunction, distinction, distinguishment,
   diversification, division, ease, eclecticism, elegance, elegancy,
   excellence, fascism, fastidiousness, favoritism, felicitousness,
   felicity, finesse, finish, fittingness, flow, flowing periods,
   fluency, good judgment, good taste, grace, gracefulness, gracility,
   graciosity, graciousness, inclination, individualization,
   individuation, inequality, inequity, insight, interest,
   intolerance, involvement, judgement, judging, judgment, judicature,
   judiciousness, keenness, know-nothingism, leaning, limpidity,
   lucidity, male chauvinist, meticulousness, minority prejudice,
   modification, naturalness, neatness, nepotism, niceness, nicety,
   one-sidedness, parti pris, partiality, particularity,
   particularization, particularness, partisanism, partisanship,
   pellucidity, penetration, perception, perceptiveness, percipience,
   perfectionism, personalization, perspicacity, perspicuity,
   picking and choosing, plainness, policy, polish, polity,
   preciseness, precisianism, precision, preference,
   preferential treatment, prejudice, priggishness, propriety,
   providence, prudence, prudentialism, prudishness, punctilio,
   punctiliousness, purism, puritanism, purity, quality, race hatred,
   race prejudice, race snobbery, racial discrimination, racialism,
   racism, red-baiting, refinement, reflection, reflectiveness,
   restraint, scrupulosity, scrupulousness, seemliness, segregation,
   selectiveness, selectivity, sense, sensitivity, separation,
   severalization, severance, sex discrimination, sexism, shrewdness,
   simplicity, smoothness, social barrier, social discrimination,
   sophistication, sound judgment, soundness of judgment,
   specialization, straightforwardness, strictness, subtlety,
   superpatriotism, taste, tastefulness, terseness, thoughtfulness,
   ultranationalism, unaffectedness, undetachment,
   undispassionateness, unfairness, unneutrality, variation, weighing,
   white power, white supremacy, wit, xenophobia