The Collaborative International Dictionary of English v.0.48:

Asymmetry \A*sym"me*try\, n. [Gr. ?; 'a priv. + ? symmetry.]
   1. Want of symmetry, or proportion between the parts of a
      thing, esp. lack of bilateral symmetry.
      [1913 Webster]

   2. (Math.) Incommensurability. [Obs.] --Barrow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

asymmetry
    n 1: (mathematics) a lack of symmetry [syn: asymmetry,
         dissymmetry, imbalance] [ant: balance,
         correspondence, symmetricalness, symmetry]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "asymmetry":
   ambiguity, ambivalence, anamorphism, anamorphosis, antinomy,
   buckle, contortion, contrariety, crookedness, detorsion, deviation,
   difference, disequilibrium, disparity, disproportion,
   disproportionateness, distortion, equivocality, gnarl, heresy,
   heterodoxy, heterogeneity, imbalance, inadequacy, incoherence,
   incommensurability, incompatibility, incongruity, inconsistency,
   inconsonance, inequality, inequity, injustice, insufficiency,
   irreconcilability, irregularity, knot, lopsidedness,
   nonconformability, nonconformity, nonuniformity, odds, overbalance,
   oxymoron, paradox, quirk, screw, self-contradiction, shortcoming,
   torsion, tortuosity, turn, twist, unbalance, unconformability,
   unconformity, unevenness, unfair discrimination, unorthodoxy,
   unsymmetry, warp, wrench, wrest, wring