The Collaborative International Dictionary of English v.0.48:

Seditious \Se*di"tious\, a.[L. seditiosus: cf. F. s['e]ditieux.]
   1. Of or pertaining to sedition; partaking of the nature of,
      or tending to excite, sedition; as, seditious behavior;
      seditious strife; seditious words.
      [1913 Webster]

   2. Disposed to arouse, or take part in, violent opposition to
      lawful authority; turbulent; factious; guilty of sedition;
      as, seditious citizens.
      [1913 Webster] -- Se*di"tious*ly, adv. --
      Se*di"tious*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

seditious
    adj 1: arousing to action or rebellion [syn: incendiary,
           incitive, inflammatory, instigative, rabble-
           rousing, seditious]
    2: in opposition to a civil authority or government [syn:
       insurgent, seditious, subversive]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "seditious":
   alienated, breakaway, contumacious, disaffected, disloyal,
   dissident, extreme, extremistic, factious, faithless, inflammatory,
   insurgent, insurrectionary, insurrectionist, lawless, mutineering,
   mutinous, perfidious, rabble-rousing, rebel, rebellious,
   refractory, revolutional, revolutionary, riotous, seditionary,
   subversive, traitorous, treacherous, treasonable, turbulent,
   turncoat, unfaithful, violent