The Collaborative International Dictionary of English v.0.48:

Unequal \Un*e"qual\, a. [Cf. Inequal.]
   1. Not equal; not matched; not of the same size, length,
      breadth, quantity, strength, talents, acquirements, age,
      station, or the like; as, the fingers are of unequal
      length; peers and commoners are unequal in rank.
      [1913 Webster]

   2. Ill balanced or matched; disproportioned; hence, not
      equitable; partial; unjust; unfair.
      [1913 Webster]

            Against unequal arms to fight in pain. --Milton.
      [1913 Webster]

            Jerome, a very unequal relator of the opinion of his
            adversaries.                          --John
                                                  Worthington.
      [1913 Webster]

            To punish me for what you make me do
            Seems much unequal.                   --Shak.
      [1913 Webster]

   3. Not uniform; not equable; irregular; uneven; as, unequal
      pulsations; an unequal poem.
      [1913 Webster]

   4. Not adequate or sufficient; inferior; as, the man was
      unequal to the emergency; the timber was unequal to the
      sudden strain.
      [1913 Webster]

   5. (Bot.) Not having the two sides or the parts symmetrical.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unequal
    adj 1: poorly balanced or matched in quantity or value or
           measure [ant: equal]
    2: lacking the requisite qualities or resources to meet a task;
       "inadequate training"; "the staff was inadequate"; "she was
       unequal to the task" [syn: inadequate, unequal] [ant:
       adequate, equal]

Moby Thesaurus II by Grady Ward, 1.0:

159 Moby Thesaurus words for "unequal":
   assorted, asymmetric, at odds, at variance, broken, capricious,
   careening, catchy, changeable, changing, choppy, contrary,
   contrasted, contrasting, departing, desultory, deviating,
   deviative, deviatory, different, differentiated, differing,
   disaccordant, disagreeing, disconnected, discontinuous, discordant,
   discrepant, discrete, discriminated, disjoined, disorderly,
   disparate, disproportionate, dissimilar, dissonant, distant,
   distinct, distinguished, divaricate, divergent, diverging, divers,
   diverse, diversified, diversiform, eccentric, erose, erratic,
   fitful, flickering, fluctuating, guttering, halting, herky-jerky,
   heteroclite, heterogeneous, ill-matched, ill-sorted, illegal,
   immethodical, impulsive, in disagreement, inaccordant, inadequate,
   incompatible, incongruous, inconsistent, inconsonant, inconstant,
   inequitable, inharmonious, iniquitous, insufficient, intermittent,
   intermitting, irreconcilable, irregular, jagged, jerky, lurching,
   many, mercurial, mismatched, motley, multifarious, mutable,
   nonconformist, nonstandard, nonsymmetrical, nonuniform, odd,
   off-balance, out of proportion, overbalanced, patchy, pluralistic,
   poles apart, poles asunder, ragged, rambling, rough, scrappy,
   separate, separated, several, skew, skewed, snatchy, spasmatic,
   spasmic, spasmodic, spastic, sporadic, spotty, staggering, unalike,
   unbalanced, uncertain, unconformable, undeserved, undue, unequable,
   unequitable, uneven, unjust, unlawful, unlike, unmeet, unmerited,
   unmethodical, unmetrical, unorthodox, unregular, unrhythmical,
   unrightful, unsettled, unsimilar, unstable, unsteady,
   unsymmetrical, unsystematic, ununiform, variable, variant, varied,
   variegated, variform, various, varying, veering, wandering,
   wavering, widely apart, wobbling, wobbly, worlds apart, wrong,
   wrongful