The Collaborative International Dictionary of English v.0.48:

Asymmetric \As`ym*met"ric\, Asymmetrical \As`ym*met"ri*cal\, a.
   [See Asymmetrous.]
   1. Incommensurable. [Obs.]
      [1913 Webster]

   2. Not symmetrical; wanting proportion; esp., not bilaterally
      symmetrical. --Huxley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

asymmetric
    adj 1: characterized by asymmetry in the spatial arrangement or
           placement of parts or components [syn: asymmetrical,
           asymmetric] [ant: symmetric, symmetrical]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "asymmetric":
   anamorphous, askew, bent, bowed, cockeyed, contorted, crazy,
   crooked, crumpled, crunched, deviative, disparate,
   disproportionate, distorted, ill-matched, ill-proportioned,
   ill-sorted, inadequate, insufficient, irregular, labyrinthine,
   lopsided, mismatched, nonsymmetric, odd, one-sided,
   out of proportion, skew, skewed, sprung, tortuous, twisted,
   unequal, uneven, unsymmetric, warped