The Collaborative International Dictionary of English v.0.48:

Treaty \Trea"ty\, n.; pl. Treaties. [OE. tretee, F. trait['e],
   LL. tractatus; cf. L. tractatus a handling, treatment,
   consultation, tractate. See Treat, and cf. Tractate.]
   1. The act of treating for the adjustment of differences, as
      for forming an agreement; negotiation. "By sly and wise
      treaty." --Chaucer.
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            He cast by treaty and by trains
            Her to persuade.                      --Spenser.
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   2. An agreement so made; specifically, an agreement, league,
      or contract between two or more nations or sovereigns,
      formally signed by commissioners properly authorized, and
      solemnly ratified by the several sovereigns, or the
      supreme power of each state; an agreement between two or
      more independent states; as, a treaty of peace; a treaty
      of alliance.
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   3. A proposal tending to an agreement. [Obs.] --Shak.
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   4. A treatise; a tract. [Obs.] --Sir T. Browne.
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Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "treaty":
   NATO, SEATO, accord, agreement, alliance, arrangement, bargain,
   capitulation, cartel, charter, compact, concord, concordat,
   contract, convention, covenant, deal, entente, entente cordiale,
   international agreement, league, mutual-defense treaty,
   nonaggression pact, pact, paction, reconciliation, settlement,
   understanding