The Collaborative International Dictionary of English v.0.48:

Factious \Fac"tious\ a. [L. factiosus: cf. F. factieux.]
   1. Given to faction; addicted to form parties and raise
      dissensions, in opposition to government or the common
      good; turbulent; seditious; prone to clamor against public
      measures or men; -- said of persons.
      [1913 Webster]

            Factious for the house of Lancaster.  --Shak.
      [1913 Webster]

   2. Pertaining to faction; proceeding from faction;
      indicating, or characterized by, faction; -- said of acts
      or expressions; as, factious quarrels.
      [1913 Webster]

            Headlong zeal or factious fury.       --Burke.
      -- Fac"tious*ly, adv. -- Fac"tious*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

factious
    adj 1: dissenting (especially dissenting with the majority
           opinion) [syn: dissentious, divisive, factious]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "factious":
   aggressive, alienated, argumentative, at loggerheads, at odds,
   bellicose, belligerent, bickering, breakaway, combative,
   conflicting, contending, contentious, contumacious, disaffected,
   discordant, disputatious, divisive, eristic, estranged, extreme,
   extremistic, factional, fighting, insurgent, insurrectionary,
   irascible, irritable, litigious, mutineering, mutinous, partisan,
   polarizing, polemic, pugnacious, quarrelsome, rebel, rebellious,
   refractory, revolutional, revolutionary, riotous, seditionary,
   seditious, shrewish, subversive, traitorous, treasonable,
   turbulent, warring, wrangling