The Collaborative International Dictionary of English v.0.48:

Deformation \Def`or*ma"tion\, n. [L. deformatio: cf. F.
   d['e]formation.]
   1. The act of deforming, or state of anything deformed. --Bp.
      Hall.
      [1913 Webster]

   2. Transformation; change of shape.
      [1913 Webster]

WordNet (r) 3.0 (2006):

deformation
    n 1: a change for the worse [syn: distortion, deformation]
    2: alteration in the shape or dimensions of an object as a
       result of the application of stress to it
    3: the act of twisting or deforming the shape of something
       (e.g., yourself) [syn: contortion, deformation]