The Collaborative International Dictionary of English v.0.48:

Aberration \Ab`er*ra"tion\, n. [L. aberratio: cf. F. aberration.
   See Aberrate.]
   1. The act of wandering; deviation, especially from truth or
      moral rectitude, from the natural state, or from a type.
      "The aberration of youth." --Hall. "Aberrations from
      theory." --Burke.
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   2. A partial alienation of reason. "Occasional aberrations of
      intellect." --Lingard.
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            Whims, which at first are the aberrations of a
            single brain, pass with heat into epidemic form.
                                                  --I. Taylor.
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   3. (Astron.) A small periodical change of position in the
      stars and other heavenly bodies, due to the combined
      effect of the motion of light and the motion of the
      observer; called annual aberration, when the observer's
      motion is that of the earth in its orbit, and daily or
      diurnal aberration, when of the earth on its axis;
      amounting when greatest, in the former case, to 20.4'',
      and in the latter, to 0.3''. Planetary aberration is
      that due to the motion of light and the motion of the
      planet relative to the earth.
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   4. (Opt.) The convergence to different foci, by a lens or
      mirror, of rays of light emanating from one and the same
      point, or the deviation of such rays from a single focus;
      called spherical aberration, when due to the spherical
      form of the lens or mirror, such form giving different
      foci for central and marginal rays; and chromatic
      aberration, when due to different refrangibilities of the
      colored rays of the spectrum, those of each color having a
      distinct focus.
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   5. (Physiol.) The passage of blood or other fluid into parts
      not appropriate for it.
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   6. (Law) The producing of an unintended effect by the
      glancing of an instrument, as when a shot intended for A
      glances and strikes B.
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   Syn: Insanity; lunacy; madness; derangement; alienation;
        mania; dementia; hallucination; illusion; delusion. See
        Insanity.
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WordNet (r) 3.0 (2006):

spherical aberration
    n 1: an optical aberration resulting in a distorted image