WordNet sense 1 (North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776):

us, America, U.S.A., USA, United States, the States, United States of America

WordNet sense 2 (the executive and legislative and judicial branches of the federal government of the United States):

United States government, U.S. government, US Government