NOUN (3)

1. loyalty to the United States and its institutions;

2. an expression that is characteristic of English as spoken by Americans;

3. a custom that is peculiar to the United States or its citizens;

The Collaborative International Dictionary of English v.0.48:

Americanism \A*mer"i*can*ism\, n.
   1. Attachment to the United States.
      [1913 Webster]

   2. A custom peculiar to the United States or to America; an
      American characteristic or idea.
      [1913 Webster]

   3. A word or phrase peculiar to the United States.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Americanism
    n 1: loyalty to the United States and its institutions
    2: an expression that is characteristic of English as spoken by
       Americans
    3: a custom that is peculiar to the United States or its
       citizens

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "Americanism":
   Anglicism, Briticism, Frenchism, Gallicism, Hibernicism, Irishism,
   Latinism, Scotticism, Yankeeism, chauvinism, flag waving, jingoism,
   love of country, nationalism, nationality, overpatriotism,
   patriotics, patriotism, ultranationalism