The Collaborative International Dictionary of English v.0.48:

Amalgamation \A*mal`ga*ma"tion\, n. [Cf. F. amalgamation.]
   1. The act or operation of compounding mercury with another
      metal; -- applied particularly to the process of
      separating gold and silver from their ores by mixing them
      with mercury. --Ure.
      [1913 Webster]

   2. The mixing or blending of different elements, races,
      societies, etc.; also, the result of such combination or
      blending; a homogeneous union. --Macaulay.
      [1913 Webster]

WordNet (r) 3.0 (2006):

amalgamation
    n 1: the combination of two or more commercial companies [syn:
         amalgamation, merger, uniting]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "amalgamation":
   Anschluss, addition, admixture, affiliation, agglomeration,
   aggregation, agreement, alignment, alliance, alloy, alloyage,
   amalgam, assimilation, association, blend, blending, cabal,
   cahoots, cartel, centralization, coadunation, coalescence,
   coalescing, coalition, colleagueship, collegialism, collegiality,
   combination, combine, combo, comminglement, commingling,
   commixture, composite, composition, compost, compound, comradeship,
   confederacy, confederation, confraternity, congeries,
   conglomeration, conjugation, conjunction, consolidating,
   consolidation, conspiracy, copartnership, copartnery, eclecticism,
   ecumenism, embodiment, encompassment, enosis, federalization,
   federation, fellowship, fraternalism, fraternity, fraternization,
   freemasonry, fusing, fusion, hookup, immixture, inclusion,
   incorporation, integration, interfusion, interlarding,
   interlardment, interminglement, intermingling, intermixture,
   joining, junction, junta, league, marriage, meld, melding, merger,
   mingling, mixing, mixture, package, package deal, partnership,
   pluralism, sodality, solidification, sorority, syncretism,
   syndication, syneresis, synthesis, tie-in, tie-up, unification,
   union, uniting, wedding