The Collaborative International Dictionary of English v.0.48:

Unite \U*nite"\, v. t. [imp. & p. p. United; p. pr. & vb. n.
   Uniting.] [L. unitus, p. p. of unire to unite, from unus
   one. See One.]
   1. To put together so as to make one; to join, as two or more
      constituents, to form a whole; to combine; to connect; to
      join; to cause to adhere; as, to unite bricks by mortar;
      to unite iron bars by welding; to unite two armies.
      [1913 Webster]

   2. Hence, to join by a legal or moral bond, as families by
      marriage, nations by treaty, men by opinions; to join in
      interest, affection, fellowship, or the like; to cause to
      agree; to harmonize; to associate; to attach.
      [1913 Webster]

            Under his great vicegerent reign abide,
            United as one individual soul.        --Milton.
      [1913 Webster]

            The king proposed nothing more than to unite his
            kingdom in one form of worship.       --Clarendon.
      [1913 Webster]

   Syn: To add; join; annex; attach. See Add.
        [1913 Webster]

WordNet (r) 3.0 (2006):

uniting
    n 1: the combination of two or more commercial companies [syn:
         amalgamation, merger, uniting]
    2: the act of making or becoming a single unit; "the union of
       opposing factions"; "he looked forward to the unification of
       his family for the holidays" [syn: union, unification,
       uniting, conjugation, jointure] [ant: disunion]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "uniting":
   accession, accompanying, accordant, addition, adjunct, adjunction,
   affixation, agglutination, agreeing, annexation, approaching,
   associate, associated, associative, asymptotic, at one with,
   attachment, augmentation, blending, centripetal, centrolineal,
   coacting, coactive, coadunate, coalescent, coalescing, coincident,
   collaborative, collective, collusive, combinative, combinatory,
   combined, combining, concerted, concomitant, concordant,
   concurrent, concurring, confluent, confocal, conjoint,
   conjunctival, conjunctive, connecting, connectional, connective,
   connivent, consilient, conspiratorial, converging, cooperant,
   cooperative, coordinate, corporational, coworking, federal,
   federative, focal, fusing, harmonious, incorporating,
   incorporative, increase, joining, joint, junction, juxtaposition,
   meeting, merging, mutually approaching, parasitic, prefixation,
   radial, radiating, reinforcement, saprophytic, suffixation,
   superaddition, superfetation, superjunction, superposition,
   supplementation, symbiotic, synchronous, synergetic, synergic,
   synergistic, tangent, tangential, unific, unifying, united