The Collaborative International Dictionary of English v.0.48:

Cabal \Ca*bal"\ (k[.a]*b[a^]l"), n. [F. cabale cabal, cabala,
   LL. cabala cabala, fr. Heb. qabb[=a]l[=e]h reception,
   tradition, mysterious doctrine, fr. q[=a]bal to take or
   receive, in Pi["e]l qibbel to adopt (a doctrine).]
   1. Tradition; occult doctrine. See Cabala. [Obs.]
      --Hakewill.
      [1913 Webster]

   2. A secret. [Obs.] "The measuring of the temple, a cabal
      found out but lately." --B. Jonson.
      [1913 Webster]

   3. A number of persons united in some close design, usually
      to promote their private views and interests in church or
      state by intrigue; a secret association composed of a few
      designing persons; a junto.
      [1913 Webster]

   Note: It so happend, by a whimsical coincidence, that in 1671
         the cabinet consisted of five persons, the initial
         letters of whose names made up the word cabal;
         Clifford, Arlington, Buckingham, Ashley, and
         Lauderdale. --Macaulay.
         [1913 Webster]

   4. The secret artifices or machinations of a few persons
      united in a close design; intrigue.
      [1913 Webster]

            By cursed cabals of women.            --Dryden.

   Syn: Junto; intrigue; plot; combination; conspiracy.

   Usage: Cabal, Combination, Faction. An association for
          some purpose considered to be bad is the idea common
          to these terms. A combination is an organized union of
          individuals for mutual support, in urging their
          demands or resisting the claims of others, and may be
          good or bad according to circumstances; as, a
          combiniation of workmen or of employers to effect or
          to prevent a change in prices. A cabal is a secret
          association of a few individuals who seek by cunning
          practices to obtain office and power. A faction is a
          larger body than a cabal, employed for selfish
          purposes in agitating the community and working up an
          excitement with a view to change the existing order of
          things. "Selfishness, insubordination, and laxity of
          morals give rise to combinations, which belong
          particularly to the lower orders of society. Restless,
          jealous, ambitious, and little minds are ever forming
          cabals. Factions belong especially to free
          governments, and are raised by busy and turbulent
          spirits for selfish purposes".          --Crabb.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cabal \Ca*bal"\, v. i. [imp. & p. p. Caballed (-b[a^]ld"); p.
   pr. & vb. n. Caballing]. [Cf. F. cabaler.]
   To unite in a small party to promote private views and
   interests by intrigue; to intrigue; to plot.
   [1913 Webster]

         Caballing still against it with the great. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cabal
    n 1: a clique (often secret) that seeks power usually through
         intrigue [syn: cabal, faction, junto, camarilla]
    2: a plot to carry out some harmful or illegal act (especially a
       political plot) [syn: conspiracy, cabal]
    v 1: engage in plotting or enter into a conspiracy, swear
         together; "They conspired to overthrow the government"
         [syn: conspire, cabal, complot, conjure,
         machinate]

Moby Thesaurus II by Grady Ward, 1.0:

157 Moby Thesaurus words for "cabal":
   Anschluss, addition, affiliation, age group, agglomeration,
   aggregation, agreement, alliance, amalgamation, artifice,
   assimilation, association, band, battalion, bevy, blend, blending,
   body, brigade, bunch, cadre, camarilla, cartel, cast, caucus, cell,
   centralization, charmed circle, circle, clan, clique,
   closed circle, club, coalescence, coalition, cohort, collusion,
   combination, combine, combo, company, complement, complicity,
   complot, composition, confederacy, confederation, congeries,
   conglomeration, conjugation, conjunction, connivance, connive,
   consolidation, conspiracy, conspire, contingent, contrivance,
   contriving, corps, coterie, counterplot, covey, covin, crew, crowd,
   deep-laid plot, detachment, detail, division, ecumenism, elite,
   elite group, embodiment, encompassment, engineering, enosis,
   faction, federalization, federation, finagling, finesse, fleet,
   frame-up, fusion, game, gang, group, grouping, groupment, hookup,
   in-group, inclusion, incorporation, ingroup, inner circle,
   integration, intrigue, junction, junta, junto, league, little game,
   machinate, machination, maneuvering, manipulation, marriage, meld,
   melding, merger, mob, movement, out-group, outfit, pack, package,
   package deal, party, peer group, phalanx, platoon, plot, plotting,
   posse, regiment, rigging, ring, salon, scheme, schemery, scheming,
   set, solidification, squad, stable, stratagem, string, syncretism,
   syndication, syneresis, synthesis, team, tie-up, tribe, trick,
   troop, troupe, underplot, unification, union, unit, we-group,
   web of intrigue, wedding, wing, wire-pulling