The Collaborative International Dictionary of English v.0.48:

Inconsistent \In`con*sist"ent\, a. [Pref. in- not + consistent:
   cf. F. inconsistant.]
   [1913 Webster]
   1. Not consistent; showing inconsistency; irreconcilable;
      contradictory, or having contradictory implications;
      discordant; at variance, esp. as regards character,
      sentiment, or action; incompatible; incongruous.
      [1913 Webster]

            Compositions of this nature . . . show that wisdom
            and virtue are far from being inconsistent with
            politeness and good humor.            --Addison.
      [1913 Webster]

   2. Not exhibiting uniformity of sentiment, steadiness to
      principle, etc.; unequal; fickle; changeable.
      [1913 Webster]

            Ah, how unjust to nature, and himself,
            Is thoughtless, thankless, inconsistent man.
                                                  --Young.

   Syn: Incompatible; incongruous; irreconcilable; discordant;
        repugnant; contradictory.

   Usage: Inconsistent, Incongruous, Incompatible. Things
          are incongruous when they are not suited to each
          other, so that their union is unbecoming; inconsistent
          when they are opposed to each other, so as render it
          improper or wrong; incompatible when they can not
          coexist, and it is therefore impossible to unite them.
          Habitual levity of mind is incongruous with the
          profession of a clergyman; it is inconsistent with his
          ordination vows; it is incompatible with his permanent
          usefulness. Incongruity attaches to the modes and
          qualities of things; incompatibility attaches to their
          essential attributes; inconsistency attaches to the
          actions, sentiments, etc., of men.
          [1913 Webster]

WordNet (r) 3.0 (2006):

inconsistent
    adj 1: displaying a lack of consistency; "inconsistent
           statements cannot both be true at the same time";
           "inconsistent with the roadmap" [ant: consistent]
    2: not capable of being made consistent or harmonious;
       "inconsistent accounts"
    3: not in agreement [syn: discrepant, inconsistent]

Moby Thesaurus II by Grady Ward, 1.0:

245 Moby Thesaurus words for "inconsistent":
   abnormal, absonant, absurd, adrift, adversative, adverse,
   adversive, afloat, aloof, alternating, amorphous, anomalous,
   antagonistic, anti, antipathetic, antithetic, antonymous, assorted,
   at cross-purposes, at odds, at variance, balancing, broken,
   capricious, changeable, changeful, changing, choppy, clashing,
   compensating, conflicting, confronting, contradictory,
   contradistinct, contrapositive, contrarious, contrary,
   contrary to reason, contrasted, contrasting, converse, counter,
   counterbalancing, counterpoised, countervailing, dead against,
   departing, desultory, detached, deviable, deviating, deviative,
   deviatory, different, differentiated, differing, disaccordant,
   disagreeing, disconnected, discontinuous, discordant, discrepant,
   discrete, discriminated, disjoined, disorderly, disparate,
   disproportionate, dissimilar, dissonant, distinct, distinguished,
   divaricate, divergent, diverging, divers, diverse, diversified,
   diversiform, dizzy, eccentric, erose, erratic, eyeball to eyeball,
   fallacious, fast and loose, faulty, fickle, fitful, flawed,
   flickering, flighty, flitting, fluctuating, freakish, gapped,
   giddy, heterogeneous, hostile, illogical, impetuous, impulsive,
   in disagreement, inaccordant, inauthentic, incoherent,
   incommensurable, incommensurate, incompatible, inconclusive,
   incongruous, inconsequent, inconsequential, inconsonant,
   inconstant, indecisive, infirm, inharmonious, inimical, invalid,
   inverse, irrational, irreconcilable, irregular, irresolute,
   irresponsible, jagged, jerky, loose, lubricious, many, mazy,
   mercurial, moody, motley, multifarious, mutable, nonadherent,
   nonadhesive, noncoherent, noncohesive, nonconformist,
   nonscientific, nonstandard, nonuniform, not following, obverse,
   open, opposed, opposing, opposite, oppositional, oppositive,
   oppugnant, out of proportion, oxymoronic, paradoxical, paralogical,
   perverse, pluralistic, poles apart, poles asunder, ragged,
   rambling, reasonless, repugnant, restless, reverse, rough, roving,
   scatterbrained, self-annulling, self-contradictory, self-refuting,
   senseless, separate, separated, several, shapeless, shifting,
   shifty, shuffling, spasmodic, spineless, sporadic, squared off,
   temperamental, tenuous, ticklish, unaccountable, unadhesive,
   unauthentic, uncertain, uncoherent, uncohesive, unconformable,
   unconnected, uncontrolled, undependable, undisciplined, unequable,
   unequal, uneven, unfixed, unjoined, unlike, unorthodox,
   unphilosophical, unpredictable, unreasonable, unreliable,
   unrestrained, unscientific, unsettled, unstable, unstable as water,
   unstaid, unsteadfast, unsteady, unsystematic, untenacious,
   ununiform, vacillating, vagrant, variable, variant, varied,
   variegated, variform, various, varying, vicissitudinary,
   vicissitudinous, volatile, wandering, wanton, wavering, wavery,
   wavy, wayward, whimsical, widely apart, wishy-washy,
   without reason, worlds apart