The Collaborative International Dictionary of English v.0.48:

Faction \Fac"tion\ (f[a^]k"sh[u^]n), n. [L. factio a doing, a
   company of persons acting together, a faction: cf. F. faction
   See Fashion.]
   1. (Anc. Hist.) One of the divisions or parties of
      charioteers (distinguished by their colors) in the games
      of the circus.
      [1913 Webster]

   2. A party, in political society, combined or acting in
      union, in opposition to the government, or state; --
      usually applied to a minority, but it may be applied to a
      majority; a combination or clique of partisans of any
      kind, acting for their own interests, especially if
      greedy, clamorous, and reckless of the common good.
      [1913 Webster]

   3. Tumult; discord; dissension.
      [1913 Webster]

            They remained at Newbury in great faction among
            themselves.                           --Clarendon.

   Syn: Combination; clique; junto. See Cabal.
        [1913 Webster]

WordNet (r) 3.0 (2006):

faction
    n 1: a clique (often secret) that seeks power usually through
         intrigue [syn: cabal, faction, junto, camarilla]
    2: a dissenting clique [syn: faction, sect]