Un'ion of So'viet So'cialist Repub'lics
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). Cap.: Moscow. Also called Russia, Soviet Union. Abbr.: U.S.S.R., USSR
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.