The Collaborative International Dictionary of English v.0.48:

Nationalism \Na"tion*al*ism\, n.
   1. The state of being national; national attachment;
      nationality.
      [1913 Webster]

   2. An idiom, trait, or character peculiar to any nation.
      [1913 Webster]

   3. National independence; the principles of the Nationalists.
      [1913 Webster]

   4. A devotion to one's country; patriotism; especially. an
      exaggerated or excessive form of patriotism; chauvinism.
      [PJC]

   5. The policy of advocating the independence of one's
      country.
      [PJC]

   6. The policy of advocating the interests of one's own
      country exclusively, regardless of effects of a country's
      actions on other countries.
      [PJC]

WordNet (r) 3.0 (2006):

nationalism
    n 1: love of country and willingness to sacrifice for it; "they
         rode the same wave of popular patriotism"; "British
         nationalism was in the air and patriotic sentiments ran
         high" [syn: patriotism, nationalism]
    2: the doctrine that your national culture and interests are
       superior to any other [ant: internationalism,
       multiculturalism]
    3: the aspiration for national independence felt by people under
       foreign domination
    4: the doctrine that nations should act independently (rather
       than collectively) to attain their goals [ant:
       internationalism]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "nationalism":
   Americanism, Anglicism, Briticism, Eisenhower Doctrine,
   Monroe Doctrine, Nixon Doctrine, Truman Doctrine, appeasement,
   balance of power, brinkmanship, chauvinism, coexistence,
   colonialism, compromise, containment, detente, deterrence,
   diplomacy, diplomatic, diplomatics, dollar diplomacy,
   dollar imperialism, expansionism, flag waving, foreign affairs,
   foreign policy, good-neighbor policy, imperialism, independence,
   internationalism, internationality, isolationism, jingoism,
   love of country, manifest destiny, militarism, nationality,
   nationhood, neocolonialism, neutralism, nonresistance, open door,
   open-door policy, overpatriotism, patriotics, patriotism,
   peace offensive, peaceful coexistence, peoplehood, preparedness,
   self-determination, self-government, shirt-sleeve diplomacy,
   shuttle diplomacy, sovereign nationhood, sovereignty,
   spheres of influence, statehood, the big stick, tough policy,
   ultranationalism, world politics