1) n. A citizen of the United States who is of a wealthy background also being heir to a sizeable fortune, typically a trust fund or inheritance to which they are entitled only because of their family's success. 2) n. A United States citizen who has inherited said monies. 3) n. A little shit kid who never has to work for anything in his life.
See also: Yuppie, Richie, LaCoste, Paris Hilton
George W. Bush is a classic example of what it means to be Amheirican.