The Collaborative International Dictionary of English v.0.48:

American \A*mer"i*can\ ([.a]*m[~e]r"[i^]*kan), a. [Named from
   Americus Vespucius.]
   1. Of or pertaining to America; as, the American continent:
      American Indians.
      [1913 Webster]

   2. Of or pertaining to the United States. "A young officer of
      the American navy." --Lyell.
      [1913 Webster]

   American ivy. See Virginia creeper.

   American Party (U. S. Politics), a party, about 1854, which
      opposed the influence of foreign-born citizens, and those
      supposed to owe allegiance to a foreign power.

   Native american Party (U. S. Politics), a party of
      principles similar to those of the American party. It
      arose about 1843, but soon died out.
      [1913 Webster]

WordNet (r) 3.0 (2006):

American Party
    n 1: a former political party in the United States; active in
         the 1850s to keep power out of the hands of immigrants and
         Roman Catholics [syn: American Party, Know-Nothing
         Party]