WordNet (r) 3.0 (2006):

USSR
    n 1: a former communist country in eastern Europe and northern
         Asia; established in 1922; included Russia and 14 other
         soviet socialist republics (Ukraine and Byelorussia and
         others); officially dissolved 31 December 1991 [syn:
         Soviet Union, Russia, Union of Soviet Socialist
         Republics, USSR]