Union of Soviet Socialist Republics

noun
1.
a former federal union of 15 constituent republics, in E Europe and W and N Asia, comprising the larger part of the former Russian Empire: dissolved in December 1991. 8,650,069 sq. mi. (22,402,200 sq. km).
Capital: Moscow.
Abbreviation: U.S.S.R., USSR.
Also called Russia, Soviet Union.
British Dictionary definitions for Union of Soviet Socialist Republics

Union of Soviet Socialist Republics

noun
1.
the official name of the former Soviet Union
Union of Soviet Socialist Republics in Culture
Union of Soviet Socialist Republics (USSR)

Official name of the former Soviet Union.