The Collaborative International Dictionary of English v.0.48:

Disagreement \Dis`a*gree"ment\ (d[i^]s`[.a]*gr[=e]"ment), n.
   [Cf. F. d['e]sagr['e]ment disagreeable circumstance,
   disagreeableness.]
   1. The state of disagreeing; a being at variance;
      dissimilitude; diversity.
      [1913 Webster]

   2. Unsuitableness; unadaptedness. [R.]
      [1913 Webster]

   3. Difference of opinion or sentiment.
      [1913 Webster]

   4. A falling out, or controversy; difference.

   Syn: Difference; diversity; dissimilitude; unlikeness;
        discrepancy; variance; dissent; misunderstanding;
        dissension; division; dispute; jar; wrangle; discord.
        [1913 Webster]

WordNet (r) 3.0 (2006):

disagreement
    n 1: a conflict of people's opinions or actions or characters
         [syn: disagreement, dissension, dissonance] [ant:
         accord, agreement]
    2: a difference between conflicting facts or claims or opinions;
       "a growing divergence of opinion" [syn: discrepancy,
       disagreement, divergence, variance]
    3: the speech act of disagreeing or arguing or disputing [ant:
       agreement]

Moby Thesaurus II by Grady Ward, 1.0:

199 Moby Thesaurus words for "disagreement":
   abnegation, agreement to disagree, alienation, altercation,
   antagonism, antipathy, antithesis, apostasy, argument, averseness,
   aversion, backwardness, ban, blackball, blackballing, clash,
   clashing, collision, complaint, conflict, confrontation,
   contention, contradiction, contradistinction, contraindication,
   contraposition, contrariety, contrast, controversy,
   counter-culture, counterposition, cross-purposes, cursoriness,
   debate, declension, declination, declinature, declining, denial,
   departure, deprivation, deviation, difference,
   difference of opinion, difficulty, dim view, disaccord,
   disaccordance, disallowance, disappointment, disapprobation,
   disapproval, disclaimer, disclamation, disconformity, discongruity,
   discontent, discontentedness, discontentment, discord, discordance,
   discordancy, discrepancy, discreteness, disenchantment, disesteem,
   disfavor, disgruntlement, disillusion, disillusionment,
   disinclination, disobedience, disparity, displeasure, dispute,
   disrelish, disrespect, dissatisfaction, dissension, dissent,
   dissentience, dissidence, dissimilarity, distaste, distinction,
   distinctness, divergence, divergency, diversity, dividedness,
   division, dropping out, exclusion, far cry, foot-dragging,
   fractiousness, grudging consent, grudgingness, heterogeneity,
   holding back, hostility, inaccordance, incompatibility,
   incongruity, inconsistency, inconsonance, indignation,
   indisposedness, indisposition, indocility, inequality,
   inharmoniousness, inharmony, inimicalness, intractableness,
   irreconcilability, lack of enthusiasm, lack of zeal,
   low estimation, low opinion, minority opinion, misunderstanding,
   mixture, mutinousness, nay, negation, negative, negative answer,
   nix, no, nolition, nonacceptance, nonagreement, nonassent,
   noncompliance, nonconcurrence, nonconformance, nonconformism,
   nonconformity, nonconsent, nonobservance, objection, obstinacy,
   odds, oppositeness, opposition, opposure, oppugnance, oppugnancy,
   originality, ostracism, otherness, perfunctoriness, perversity,
   polarity, polarization, protest, quarrel, recalcitrance,
   recalcitrancy, recantation, recusance, recusancy, refractoriness,
   refusal, rejection, reluctance, renitence, renitency, repudiation,
   repugnance, resistance, retention, rhubarb, secession,
   separateness, showdown, slowness, strife, stubbornness, sulk,
   sulkiness, sulks, sullenness, thumbs-down, turndown, unconformity,
   underground, unenthusiasm, unhappiness, unlikeness, unorthodoxy,
   unwillingness, variance, variation, variegation, variety,
   withdrawal, withholding