The Collaborative International Dictionary of English v.0.48:

Contradiction \Con`tra*dic"tion\, n. [L. contradictio answer,
   objection: cf. F. contradiction.]
   1. An assertion of the contrary to what has been said or
      affirmed; denial of the truth of a statement or assertion;
      contrary declaration; gainsaying.
      [1913 Webster]

            His fair demands
            Shall be accomplished without contradiction. --Shak.
      [1913 Webster]

   2. Direct opposition or repugnancy; inconsistency;
      incongruity or contrariety; one who, or that which, is
      inconsistent.
      [1913 Webster]

            can he make deathless death? That were to make
            Strange contradiction.                --Milton.
      [1913 Webster]

            We state our experience and then we come to a manly
            resolution of acting in contradiction to it.
                                                  --Burke.
      [1913 Webster]

            Both parts of a contradiction can not possibly be
            true.                                 --Hobbes.
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            Of contradictions infinite the slave. --Wordsworth.
      [1913 Webster]

   Principle of contradiction (Logic), the axiom or law of
      thought that a thing cannot be and not be at the same
      time, or a thing must either be or not be, or the same
      attribute can not at the same time be affirmed and and
      denied of the same subject; also called the law of the
      excluded middle.

   Note: It develops itself in three specific forms which have
         been called the "Three Logical Axioms." First, "A is
         A." Second, "A is not Not-A" Third, "Everything is
         either A or Not-A."
         [1913 Webster]

WordNet (r) 3.0 (2006):

contradiction
    n 1: opposition between two conflicting forces or ideas
    2: (logic) a statement that is necessarily false; "the statement
       `he is brave and he is not brave' is a contradiction" [syn:
       contradiction, contradiction in terms]
    3: the speech act of contradicting someone; "he spoke as if he
       thought his claims were immune to contradiction"

Moby Thesaurus II by Grady Ward, 1.0:

159 Moby Thesaurus words for "contradiction":
   abjuration, abjurement, abrogation, absolute contradiction,
   annulment, answer, antagonism, antipathy, antithesis,
   argumentation, backlash, bucking, challenge, chucking,
   chucking out, clashing, collision, complete answer, conflict,
   confounding, confrontation, confutation, contempt, contention,
   contradistinction, contraindication, contraposition, contrariety,
   contrary assertion, contrast, contravention, contraversion,
   controversion, controversy, counteraction, countering,
   counterposition, counterworking, crankiness, cross-purposes,
   crosscurrent, crossing, crotchetiness, declination, declining,
   demolition, denial, despisal, despising, difference, disaccord,
   disaccordance, disaffirmation, disagreement, disallowance,
   disapproval, disavowal, discard, disclaimer, disclamation, discord,
   discordance, discordancy, discounting, discrediting, discrepancy,
   disharmony, dismissal, disownment, disparity, disproof, disregard,
   dissension, dissent, dissidence, dissonance, disunion, disunity,
   divergence, diversity, effective rejoinder, exception, exclusion,
   faction, forswearing, friction, gainsaying, head wind, hostility,
   ignoring, impugnation, impugnment, inaccordance, inconsistency,
   inequality, inimicalness, interference, jarring, kick, negation,
   nonacceptance, nonapproval, nonconformity, nonconsideration,
   nullification, opposing, oppositeness, opposition, opposure,
   oppugnance, oppugnancy, oppugnation, overthrow, overthrowal,
   passing by, perverseness, perversity, polarity, putting away,
   putting out, reaction, rebuff, rebutment, rebuttal, recalcitrance,
   recantation, recoil, refusal, refutal, refutation, rejection,
   renitency, renouncement, renunciation, repercussion, repudiation,
   repugnance, repulse, resistance, retractation, retraction,
   revocation, revolt, scouting, showdown, spurning, squelch,
   standing against, subversion, swimming upstream, throwing out,
   traversal, turning out, undercurrent, undermining,
   unharmoniousness, upset, upsetting, variance



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CONTRADICTION. The incompatibility, contrariety, and evident opposition of
two ideas, which are the subject of one and the same proposition.
     2. In general, when a party accused of a crime contradicts himself, it
is presumed he does so because he is guilty for truth does not contradict
itself, and is always consistent, whereas falsehood is in general
inconsistent and the truth of some known facts will contradict the falsehood
of those which are falsely alleged to be true. But there must still be much
caution used by the judge, as there may be sometimes apparent contradictions
which arise either from the timidity, the ignorance, or the inability of the
party to explain himself, when in fact he tells the truth.
    3. When a witness contradicts himself as to something which is important
in the case, his testimony will be much weakened, or it may be entirely
discredited and when he relates a story of facts which he alleges passed
only in his presence, and he is contradicted as to other facts which are
known to others, his credit will be much impaired.
     4. When two witnesses, or other persons, state things directly opposed
to each other, it is the duty of the judge or jury to reconcile these
apparent contradictions; but when this cannot be done, the more improbable
statement must be rejected; or, if both are entitled to the same credit,
then the matter is as if no proof had been given. See Circumstances.