WordNet (r) 3.0 (2006):

NATO
    n 1: an international organization created in 1949 by the North
         Atlantic Treaty for purposes of collective security [syn:
         North Atlantic Treaty Organization, NATO]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "NATO":
   AL, ANZUS Council, ASPAC, Arab League, BIS, British Commonwealth,
   CACM, CENTO, Central Treaty Organization, Colombo Plan,
   Common Market, Commonwealth of Nations, Council of Europe, ECSC,
   EEC, EFTA, Euratom, European Economic Community, French Community,
   ICRC, Interpol, LAFTA, Nordic Council, OAS, OAU, OCAM, OECD, OPEC,
   SEATO, WCC, Warsaw Pact, alliance, capitulation, cartel, concord,
   concordat, convention, entente, entente cordiale,
   international agreement, league, mutual-defense treaty,
   nonaggression pact, paction, treaty