The Collaborative International Dictionary of English v.0.48:

Distinction \Dis*tinc"tion\, n. [L. distinctio: cf. F.
   distinction.]
   1. A marking off by visible signs; separation into parts;
      division. [Obs.]
      [1913 Webster]

            The distinction of tragedy into acts was not known.
                                                  --Dryden.
      [1913 Webster]

   2. The act of distinguishing or denoting the differences
      between objects, or the qualities by which one is known
      from others; exercise of discernment; discrimination.
      [1913 Webster]

            To take away therefore that error, which confusion
            breedeth, distinction is requisite.   --Hooker.
      [1913 Webster]

   3. That which distinguishes one thing from another;
      distinguishing quality; sharply defined difference; as,
      the distinction between real and apparent good.
      [1913 Webster]

            The distinction betwixt the animal kingdom and the
            inferior parts of matter.             --Locke.
      [1913 Webster]

   4. Estimation of difference; regard to differences or
      distinguishing circumstance.
      [1913 Webster]

            Maids, women, wives, without distinction, fall.
                                                  --Dryden.
      [1913 Webster]

   5. Conspicuous station; eminence; superiority; honorable
      estimation; as, a man of distinction.
      [1913 Webster]

            Your country's own means of distinction and defense.
                                                  --D. Webster.

   Syn: Difference; variation, variety; contrast; diversity;
        contrariety; disagreement; discrimination; preference;
        superiority; rank; note; eminence.
        [1913 Webster]

WordNet (r) 3.0 (2006):

distinction
    n 1: a discrimination between things as different and distinct;
         "it is necessary to make a distinction between love and
         infatuation" [syn: differentiation, distinction]
    2: high status importance owing to marked superiority; "a
       scholar of great eminence" [syn: eminence, distinction,
       preeminence, note]
    3: a distinguishing quality; "it has the distinction of being
       the cheapest restaurant in town"
    4: a distinguishing difference; "he learned the distinction
       between gold and lead"

Moby Thesaurus II by Grady Ward, 1.0:

212 Moby Thesaurus words for "distinction":
   Atticism, accolade, account, alteration, analysis, anatomization,
   ancestry, appropriateness, aristocracy, aristocraticalness,
   atomization, award, badge, bays, birth, blood, blue blood,
   celebrity, change, characterization, chasteness, chastity, clarity,
   classicalism, classicism, clearness, comeliness, consequence,
   conspicuousness, contradistinction, contrariety, contrast,
   correctness, credit, decoration, definition, delicacy,
   delicate distinction, demarcation, departure, description,
   desynonymization, deviation, difference, differencing, differentia,
   differential, differentiation, dignity, directness, disaccord,
   disaccordance, disagreement, disconformity, discongruity,
   discordance, discrepancy, discreteness, discrimination,
   disequalization, disjunction, disparity, dissemblance, dissent,
   dissimilarity, dissimilitude, dissonance, distinctiveness,
   distinctness, distinguishment, divergence, divergency,
   diversification, diversity, dividing line, division, ease,
   elegance, elegancy, elevation, eminence, esteem, exaltation,
   excellence, fame, far cry, felicitousness, felicity, fine point,
   finish, fittingness, flow, flowing periods, fluency, genteelness,
   gentility, glory, good taste, grace, gracefulness, gracility,
   grandeur, great honor, greatness, hairline, hairsplitting, heroism,
   heterogeneity, high mightiness, honor, honorable descent,
   illustriousness, importance, inaccordance, incompatibility,
   incongruity, inconsistency, inconsonance, individualization,
   individuation, inequality, inharmoniousness, inharmony,
   irreconcilability, kudos, laurels, limpidity, loftiness, lucidity,
   magnanimity, majesty, margin, mark, memorability, merit,
   microscopic distinction, mixture, modification, narrow margin,
   naturalness, neatness, nice distinction, nicety, nobility,
   noble birth, nobleness, nonconformity, notability, note,
   noteworthiness, nuance, odds, opposition, ornament, otherness,
   outstandingness, particle of difference, particularization,
   pellucidity, personalization, perspicuity, plainness,
   point of difference, polish, preeminence, prestige, prominence,
   propriety, purity, quality, rank, refinement, remarkableness,
   renown, reputation, repute, restraint, royalty, salience,
   seemliness, segregation, separateness, separation, severalization,
   severance, shade of difference, significance, simplicity,
   smoothness, specialization, straightforwardness, sublimity,
   subtle distinction, subtlety, supereminence, superiority, taste,
   tastefulness, terseness, trichoschistism, unaffectedness,
   unconformity, uniqueness, unlikeness, unorthodoxy, value, variance,
   variation, variegation, variety, wide margin, worth