The Collaborative International Dictionary of English v.0.48:

Sedition \Se*di"tion\, n. [OE. sedicioun, OF. sedition, F.
   s['e]dition, fr. L. seditio, originally, a going aside;
   hence, an insurrectionary separation; pref. se-, sed-, aside
   + itio a going, fr. ire, itum, to go. Cf. Issue.]
   1. The raising of commotion in a state, not amounting to
      insurrection; conduct tending to treason, but without an
      overt act; excitement of discontent against the
      government, or of resistance to lawful authority.
      [1913 Webster]

            In soothing them, we nourish 'gainst our senate
            The cockle of rebellion, insolence, sedition.
                                                  --Shak.
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            Noisy demagogues who had been accused of sedition.
                                                  --Macaulay.
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   2. Dissension; division; schism. [Obs.]
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            Now the works of the flesh are manifest, . . .
            emulations, wrath, strife, seditions, heresies.
                                                  --Gal. v. 19,
                                                  20.
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   Syn: Insurrection; tumult; uproar; riot; rebellion; revolt.
        See Insurrection.
        [1913 Webster]

WordNet (r) 3.0 (2006):

sedition
    n 1: an illegal action inciting resistance to lawful authority
         and tending to cause the disruption or overthrow of the
         government

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "sedition":
   action, agitation, alienation, collaboration, coup, disaffection,
   estrangement, extremism, factiousness, fifth-column activity,
   fomentation, fraternization, high treason, instigation, insurgence,
   insurgency, insurgentism, insurrection, insurrectionism,
   lese majesty, misprision of treason, mutinousness, mutiny,
   petty treason, protest, putsch, quislingism, rabble-rousing,
   rebellion, rebelliousness, revolt, revolution, riotousness,
   seditiousness, stirring up, strike, subversiveness, traitorousness,
   treachery, treason, treasonableness, uprising, whipping up



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

SEDITION, crimes. The raising commotions or disturbances in the state; it is
a revolt against legitimate authority, Ersk. Princ. Laws, Scotl. b. 4, t. 4,
s. 14; Dig. Lib. 49, t. 16, 1. 3, Sec. 19.
     2. The distinction between sedition and treason consists in this, that
though its ultimate object is a violation of the public peace, or at least
such a course of measures as evidently engenders it, yet it does not aim at
direct and open violence against the laws, or the subversion of the
constitution. Alis. Crim. Law of Scotl. 580.
     3. The. obnoxious and obsolete act of July 14, 1798, 1 Story's Laws U.
S. 543, was called the sedition law, because its professed object was to
prevent disturbances.
     4. In the Scotch law, sedition is either verbal or real. Verbal is
inferred from the uttering of words tending to create discord between the
king and his people; real sedition is generally committed by convocating
together any considerable number of people, without lawful authority, under
the pretence of redressing some public grievance, to the disturbing of the
public peace. 1 Ersk. ut supra.