The Collaborative International Dictionary of English v.0.48:

Distortion \Dis*tor"tion\, n. [L. distortio: cf. F. distortion.]
   1. The act of distorting, or twisting out of natural or
      regular shape; a twisting or writhing motion; as, the
      distortions of the face or body.
      [1913 Webster]

   2. A wresting from the true meaning. --Bp. Wren.
      [1913 Webster]

   3. The state of being distorted, or twisted out of shape or
      out of true position; crookedness; perversion.
      [1913 Webster]

   4. (Med.) An unnatural deviation of shape or position of any
      part of the body producing visible deformity.
      [1913 Webster]

WordNet (r) 3.0 (2006):

distortion
    n 1: a change for the worse [syn: distortion, deformation]
    2: a shape resulting from distortion [syn: distorted shape,
       distortion]
    3: an optical phenomenon resulting from the failure of a lens or
       mirror to produce a good image [syn: aberration,
       distortion, optical aberration]
    4: a change (usually undesired) in the waveform of an acoustic
       or analog electrical signal; the difference between two
       measurements of a signal (as between the input and output
       signal); "heavy metal guitar players use vacuum tube
       amplifiers to produce extreme distortion"
    5: the act of distorting something so it seems to mean something
       it was not intended to mean [syn: distortion,
       overrefinement, straining, torture, twisting]
    6: the mistake of misrepresenting the facts