The Collaborative International Dictionary of English v.0.48:

Coalition \Co`a*li"tion\, n. [LL. coalitio: cf. F. coalition.
   See Coalesce.]
   1. The act of coalescing; union into a body or mass, as of
      separate bodies or parts; as, a coalition of atoms.
      --Bentley.
      [1913 Webster]

   2. A combination, for temporary purposes, of persons,
      parties, or states, having different interests.
      [1913 Webster]

            A coalition of the puritan and the blackleg. --J.
                                                  Randolph.
      [1913 Webster]

            The coalition between the religious and worldly
            enemies of popery.                    --Macaulay.

   Syn: Alliance; confederation; confederacy; league;
        combination; conjunction; conspiracy; union.
        [1913 Webster]

WordNet (r) 3.0 (2006):

coalition
    n 1: an organization of people (or countries) involved in a pact
         or treaty [syn: alliance, coalition, alignment,
         alinement] [ant: nonalignment, nonalinement]
    2: the state of being combined into one body [syn: coalition,
       fusion]
    3: the union of diverse things into one body or form or group;
       the growing together of parts [syn: coalescence,
       coalescency, coalition, concretion, conglutination]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "coalition":
   Anschluss, Bund, Rochdale cooperative, addition, affiliation,
   agglomeration, aggregation, agreement, alignment, alliance,
   amalgamation, anschluss, assemblage, assimilation, association,
   axis, band, blend, blending, bloc, body, cabal, cahoots, cartel,
   centralization, coadunation, coalescence, colleagueship, college,
   collegialism, collegiality, combination, combine, combo,
   common market, communist front, composition, comradeship,
   confederacy, confederation, confraternity, congeries,
   conglomeration, conjugation, conjunction, consolidation,
   conspiracy, consumer cooperative, cooperative, cooperative society,
   copartnership, copartnery, corps, council, credit union,
   customs union, economic community, ecumenism, embodiment,
   encompassment, enosis, faction, federalization, federation,
   fellowship, fraternalism, fraternity, fraternization,
   free trade area, freemasonry, front, fusion, gang,
   grass-roots movement, ground swell, group, grouping, hookup,
   inclusion, incorporation, integration, junction, junta, league,
   machine, marriage, meld, melding, mergence, merger, merging, mob,
   movement, package, package deal, partnership, party,
   political front, political machine, popular front, ring, society,
   sodality, solidification, sorority, syncretism, syndication,
   syneresis, synthesis, tie-in, tie-up, unification, union,
   wedding



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

COALITION, French law. By this word is understood an unlawful agreement
among several persons, not to do a thing except on some conditions agreed
upon.
     2. The most usual coalitions are, 1st. those which take place among
master workmen, to reduce, diminish or fix at a low rate the wages of
journeymen and other workmen; 2d. those among workmen or journeymen, not to
work except at a certain price. These offences are punished by fine and
imprisonment. Dict. de Police, h.t. In our law this offence is known by the
name of conspiracy. (q.v.)