The Collaborative International Dictionary of English v.0.48:

Aberrant \Ab*er"rant\, a. [L. aberrans, -rantis, p. pr. of
   aberrare. See Aberr.]
   1. Wandering; straying from the right way.
      [1913 Webster]

   2. (Biol.) Deviating from the ordinary or natural type;
      exceptional; abnormal.
      [1913 Webster]

            The more aberrant any form is, the greater must have
            been the number of connecting forms which, on my
            theory, have been exterminated.       --Darwin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

aberrant
    adj 1: markedly different from an accepted norm; "aberrant
           behavior"; "deviant ideas" [syn: aberrant, deviant,
           deviate]
    n 1: one whose behavior departs substantially from the norm of a
         group

Moby Thesaurus II by Grady Ward, 1.0:

137 Moby Thesaurus words for "aberrant":
   aberrative, abnormal, abominable, abroad, adrift, all abroad,
   all off, all wrong, amiss, amorphous, anomalistic, anomalous,
   askew, astray, at fault, atrocious, atypical, awry,
   beside the mark, circuitous, corrupt, criminal, deceptive,
   defective, delinquent, delusive, departing, desultory, deviant,
   deviating, deviational, deviative, deviatory, devious, different,
   digressive, discursive, disgraceful, disparate, distorted,
   divergent, eccentric, errant, erratic, erring, erroneous, evil,
   exceptional, excursive, fallacious, false, faultful, faulty,
   flawed, formless, hardly the thing, heretical, heteroclite,
   heterodox, heteromorphic, ignominious, illegal, illogical,
   illusory, improper, inappropriate, incorrect, indecorous, indirect,
   infamous, irregular, labyrinthine, mazy, meandering, not done,
   not right, not the thing, not true, odd, off, off the track,
   off-base, off-color, out, out-of-line, out-of-the-way, peccant,
   peculiar, perverse, perverted, planetary, preternatural, rambling,
   roving, sacrilegious, scandalous, self-contradictory, serpentine,
   shameful, shameless, shapeless, shifting, sinful, snaky, strange,
   stray, straying, subnormal, swerving, terrible, turning, twisting,
   undirected, undue, unfactual, unfit, unfitting, unlawful,
   unnatural, unorthodox, unproved, unrepresentative, unrighteous,
   unseemly, unsuitable, untrue, untypical, unusual, vagrant, veering,
   wandering, wicked, wide, winding, wrong, wrongful, zigzag