Source : Webster's Revised Unabridged Dictionary (1913)

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

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

   3. A word or phrase peculiar to the United States.

Source : WordNet®

Americanism
     n 1: loyalty to the USA 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