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]