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]