The Collaborative International Dictionary of English v.0.48:

Abnormal \Ab*nor"mal\, a. [For earlier anormal, F. anormal, LL.
   anormalus for anomalus, Gr. ?. Confused with L. abnormis. See
   Anomalous, Abnormous, Anormal.]
   Not conformed to rule or system; deviating from the type;
   anomalous; irregular. "That deviating from the type;
   anomalous; irregular. " --Froude.
   [1913 Webster]

WordNet (r) 3.0 (2006):

abnormal
    adj 1: not normal; not typical or usual or regular or conforming
           to a norm; "abnormal powers of concentration"; "abnormal
           amounts of rain"; "abnormal circumstances"; "an abnormal
           interest in food" [syn: abnormal, unnatural] [ant:
           normal]
    2: departing from the normal in e.g. intelligence and
       development; "they were heartbroken when they learned their
       child was abnormal"; "an abnormal personality" [ant:
       normal]
    3: much greater than the normal; "abnormal profits"; "abnormal
       ambition"

Moby Thesaurus II by Grady Ward, 1.0:

155 Moby Thesaurus words for "abnormal":
   aberrant, abominable, absurd, amorphous, anomalistic, anomalous,
   atrocious, atypical, bereft of reason, brainsick, crackbrained,
   cracked, crank, crankish, cranky, crazed, crazy, criminal,
   crotchety, daft, delinquent, deluded, demented, deprived of reason,
   deranged, deviant, deviative, different, disgraceful, disoriented,
   disproportionate, distraught, divergent, dotty, eccentric, erratic,
   evil, exceptional, fey, flaky, flighty, formless, freakish, funny,
   hallucinated, hardly the thing, heteroclite, heteromorphic,
   idiocratic, idiosyncratic, ignominious, illegal, improper,
   inappropriate, incoherent, incommensurable, incommensurate,
   incompatible, incongruous, inconsequent, inconsistent, inconsonant,
   incorrect, indecorous, infamous, insane, irrational,
   irreconcilable, irregular, kinky, kooky, loco, lunatic, mad,
   maddened, maggoty, manic, mazed, mental, mentally deficient,
   meshuggah, moon-struck, non compos, non compos mentis,
   not all there, not done, not right, not the thing, nutty, odd,
   oddball, of unsound mind, off, off-base, off-color, off-key,
   out of proportion, out-of-line, oxymoronic, paradoxical, peculiar,
   preternatural, psycho, queer, quirky, reasonless, sacrilegious,
   scandalous, screwball, screwy, self-contradictory, senseless,
   shameful, shameless, shapeless, sick, sinful, singular, stark-mad,
   stark-staring mad, strange, stray, straying, subnormal, terrible,
   tetched, touched, twisted, unbalanced, unconventional, uncustomary,
   undue, unfit, unfitting, unhinged, unlawful, unnatural, unregular,
   unrepresentative, unrighteous, unsane, unseemly, unsettled,
   unsound, unsuitable, untypical, unusual, unwonted, wacky,
   wandering, whimsical, wicked, witless, wrong, wrongful



The Devil's Dictionary (1881-1906):

ABNORMAL, adj.  Not conforming to standard.  In matters of thought and
conduct, to be independent is to be abnormal, to be abnormal is to be
detested.  Wherefore the lexicographer adviseth a striving toward the
straiter [sic] resemblance of the Average Man than he hath to himself.
Whoso attaineth thereto shall have peace, the prospect of death and
the hope of Hell.