The Collaborative International Dictionary of English v.0.48:

Disagree \Dis`a*gree"\ (d[i^]s`[.a]*gr[=e]"), v. i. [imp. & p.
   p. Disagreed (d[i^]s`[.a]*gr[=e]d"); p. pr. & vb. n.
   Disagreeing.] [Pref. dis- + agree: cf. F. d['e]sagr['e]er
   to displease.]
   1. To fail to accord; not to agree; to lack harmony; to
      differ; to be unlike; to be at variance.
      [1913 Webster]

            They reject the plainest sense of Scripture, because
            it seems to disagree with what they call reason.
                                                  --Atterbury.
      [1913 Webster]

   2. To differ in opinion; to hold discordant views; to be at
      controversy; to quarrel.
      [1913 Webster]

            Who shall decide, when doctors disagree? --Pope.
      [1913 Webster]

   3. To be unsuited; to have unfitness; as, medicine sometimes
      disagrees with the patient; food often disagrees with the
      stomach or the taste.
      [1913 Webster]

   Note: Usually followed by with, sometimes by to, rarely by
         from; as, I disagree to your proposal.

   Syn: To differ; vary; dissent.
        [1913 Webster]

WordNet (r) 3.0 (2006):

disagree
    v 1: be of different opinions; "I beg to differ!"; "She
         disagrees with her husband on many questions" [syn:
         disagree, differ, dissent, take issue] [ant:
         agree, concord, concur, hold]
    2: be different from one another [syn: disagree, disaccord,
       discord] [ant: agree, check, correspond, fit,
       gibe, jibe, match, tally]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "disagree":
   agree to differ, agree to disagree, argue, be at cross-purposes,
   be at variance, be distinct, be distinguished, be in dissent,
   be unmoved, be unwilling, beg off, beg to differ, bicker, break,
   break off, clash, clash with, collide, conflict, conflict with,
   contend, contest, contradict, contrast with, counter, debate,
   decline, decline to accept, depart from, deviate from, differ,
   differ in opinion, disaccord, disaccord with, disagree with,
   disallow, disclaim, discord, discord with, dispute, dissent,
   dissent from, divaricate from, diverge, diverge from, divide,
   divide on, drop out, fall out, fight, hold opposite views,
   hold out against, jangle, jar, jar with, jostle, mismatch, mismate,
   misunderstand one another, negate, negative, not accord with,
   not agree, not buy, not consent, not get along, not hear of,
   not square with, not think of, object, oppose, pull different ways,
   quarrel, refuse, refuse consent, reject, repudiate,
   resist entreaty, resist persuasion, say nay, say no, secede,
   squabble, stand aloof, stand apart, stand over against,
   take exception, take issue, turn down, vary, vote nay,
   vote negatively, withdraw, withhold assent, wrangle