The Collaborative International Dictionary of English v.0.48:

Anomaly \A*nom"a*ly\, n.; pl. Anomalies. [L. anomalia, Gr. ?.
   See Anomalous.]
   1. Deviation from the common rule; an irregularity; anything
      anomalous.
      [1913 Webster]

            We are enabled to unite into a consistent whole the
            various anomalies and contending principles that are
            found in the minds and affairs of men. --Burke.
      [1913 Webster]

            As Professor Owen has remarked, there is no greater
            anomaly in nature than a bird that can not fly.
                                                  --Darwin.
      [1913 Webster]

   2. (Astron.)
      (a) The angular distance of a planet from its perihelion,
          as seen from the sun. This is the true anomaly. The
          eccentric anomaly is a corresponding angle at the
          center of the elliptic orbit of the planet. The mean
          anomaly is what the anomaly would be if the planet's
          angular motion were uniform.
      (b) The angle measuring apparent irregularities in the
          motion of a planet.
          [1913 Webster]

   3. (Nat. Hist.) Any deviation from the essential
      characteristics of a specific type.
      [1913 Webster]

WordNet (r) 3.0 (2006):

anomaly
    n 1: deviation from the normal or common order or form or rule
         [syn: anomaly, anomalousness]
    2: a person who is unusual [syn: anomaly, unusual person]
    3: (astronomy) position of a planet as defined by its angular
       distance from its perihelion (as observed from the sun)

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "anomaly":
   aberrance, aberrancy, aberration, abnormality, abnormity,
   amorphism, anomalism, anomalousness, conceit, conversation piece,
   crackpotism, crank, crankiness, crankism, crosspatch, crotchet,
   crotchetiness, curio, curiosity, derangement, deviancy, deviation,
   difference, differentness, divergence, dottiness, eccentricity,
   erraticism, erraticness, exception, freak, freakiness,
   freakishness, heteromorphism, idiocrasy, idiosyncrasy,
   improbability, impropriety, inadmissibility, inapplicability,
   inappositeness, inappropriateness, inaptitude, inaptness,
   individualist, infelicity, inferiority, inner-directed person,
   irregularity, irrelevance, irrelevancy, kink, maggot,
   maladjustment, mannerism, mesalliance, misalliance, misfit,
   misjoinder, misjoining, mismatch, monstrosity, museum piece,
   naysayer, nonconformist, nonconformity, nonesuch, oddball, oddity,
   peculiarity, prodigiosity, prodigy, queerness, quip, quirk,
   quirkiness, rarity, singularity, sport, strange thing, strangeness,
   subnormality, superiority, teratism, trick, twist, uncongeniality,
   unconventionality, unfitness, unnaturalism, unnaturalness,
   unsuitability, whim, whimsicality, whimsy