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.
      [1913 Webster]

   2. A partial alienation of reason. "Occasional aberrations of
      intellect." --Lingard.
      [1913 Webster]

            Whims, which at first are the aberrations of a
            single brain, pass with heat into epidemic form.
                                                  --I. Taylor.
      [1913 Webster]

   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.
      [1913 Webster]

   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.
      [1913 Webster]

   5. (Physiol.) The passage of blood or other fluid into parts
      not appropriate for it.
      [1913 Webster]

   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.
      [1913 Webster]

   Syn: Insanity; lunacy; madness; derangement; alienation;
        mania; dementia; hallucination; illusion; delusion. See
        Insanity.
        [1913 Webster]

WordNet (r) 3.0 (2006):

aberration
    n 1: a state or condition markedly different from the norm [syn:
         aberrance, aberrancy, aberration, deviance]
    2: a disorder in one's mental state
    3: an optical phenomenon resulting from the failure of a lens or
       mirror to produce a good image [syn: aberration,
       distortion, optical aberration]

Moby Thesaurus II by Grady Ward, 1.0:

224 Moby Thesaurus words for "aberration":
   aberrance, aberrancy, abet, abnormality, abnormity, alienation,
   amorphism, anomalism, anomalousness, anomaly, bend, bias,
   brain damage, brainsickness, branching off, centrifugence,
   circuitousness, clouded mind, conceit, corner, crackpotism, crank,
   crankiness, crankism, craziness, crook, crosswiseness, crotchet,
   crotchetiness, curiosity, curve, daftness, decentralization,
   declination, defectiveness, deflection, deflexure, delusion,
   dementedness, dementia, departure, deployment, derangement, detour,
   deviance, deviancy, deviation, deviousness, diagonality,
   difference, differentness, digression, discursion, disorientation,
   distortion, distraction, divagation, divarication, divergence,
   divergency, diversion, division, dogleg, dottiness, double, drift,
   drifting, eccentricity, errancy, errantry, erraticism, erraticness,
   erroneousness, error, excursion, excursus, exorbitation,
   fallaciousness, fallacy, falseness, falsity, fanning, fanning out,
   fault, faultiness, flaw, flawedness, folie, foment, freakiness,
   freakishness, furor, hairpin, hamartia, heresy, heterodoxy,
   heteromorphism, idiocrasy, idiosyncrasy, illusion, indirection,
   indirectness, inferiority, insaneness, insanity, instigate,
   irrationality, irregularity, kink, loss of mind, loss of reason,
   lunacy, madness, maggot, mania, mannerism, mental deficiency,
   mental derangement, mental disease, mental disorder,
   mental disturbance, mental illness, mental instability,
   mental sickness, mind overthrown, mindsickness, misapplication,
   misconstruction, misdoing, misfeasance, misinterpretation,
   misjudgment, mistake, monstrosity, nonconformity, obliqueness,
   obliquity, oddity, oddness, peccancy, peculiarity, pererration,
   perversion, pixilation, possession, prodigy, provoke, psychopathy,
   queerness, quip, quirk, quirkiness, rabidness, raise, rambling,
   rarity, reasonlessness, self-contradiction, senselessness,
   separation, set, set on, shattered mind, sheer, shift, shifting,
   shifting course, shifting path, sick mind, sickness, sin,
   sinfulness, singularity, skew, skewness, slant, slip, splaying,
   spread, spreading, spreading out, squint, stir up, strangeness,
   straying, subnormality, superiority, sweep, swerve, swerving,
   swinging, tack, teratism, transverseness, trick, turn, turning,
   twist, unbalance, unbalanced mind, unconventionality, unnaturalism,
   unnaturalness, unorthodoxy, unsaneness, unsound mind, unsoundness,
   unsoundness of mind, untrueness, untruth, untruthfulness, vagary,
   variation, veer, wandering, warp, whim, whimsicality, whimsy,
   witlessness, wrong, wrongness, yaw, zigzag