The Collaborative International Dictionary of English v.0.48:

Unsymmetrical \Un`sym*met"ric*al\, a.
   1. Wanting in symmetry, or due proportion pf parts.
      [1913 Webster]

   2. (Biol.) Not symmetrical; being without symmetry, as the
      parts of a flower when similar parts are of different size
      and shape, or when the parts of successive circles differ
      in number. See Symmetry.
      [1913 Webster]

   3. (Chem.) Being without symmetry of chemical structure or
      relation; as, an unsymmetrical carbon atom.
      [1913 Webster]

   Unsymmetrical carbon atom (Chem.), one which is united at
      once to four different atoms or radicals. This condition
      usually occasions physical isomerism, with the attendant
      action on polarized light.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unsymmetrical
    adj 1: lacking symmetry [syn: unsymmetric, unsymmetrical]
    2: having unsymmetrical parts or unequal dimensions or
       measurements [syn: anisometric, unsymmetrical]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "unsymmetrical":
   aimless, amorphous, anamorphous, askew, asymmetric, bent, bowed,
   capricious, casual, cockeyed, contorted, crazy, crooked, crumpled,
   crunched, desultory, deviative, disarticulated, discontinuous,
   disjunct, disordered, dispersed, disproportionate, distorted,
   erratic, fitful, formless, frivolous, gratuitous, haphazard,
   hit-or-miss, immethodical, inchoate, incoherent, indiscriminate,
   irregular, labyrinthine, lopsided, meaningless, misshapen,
   nonsymmetric, nonsymmetrical, nonsystematic, nonuniform,
   off-balance, one-sided, orderless, overbalanced, planless,
   promiscuous, random, senseless, shapeless, spasmodic, sporadic,
   sprung, straggling, straggly, systemless, tortuous, twisted,
   unarranged, unclassified, undirected, unequal, uneven, ungraded,
   unjoined, unmethodical, unordered, unorganized, unsorted,
   unsymmetric, unsystematic, ununiform, vague, wandering, warped