Union of Soviet Socialist Republics Commonly called Soviet Union or Russia Abbr. USSR A former country of northern Eurasia with coastlines on the Baltic and Black Seas and the Arctic and Pacific Oceans. Established by the union (1922) of the Russian SFSR (proclaimed after the Russian Revolution of 1917) and various other soviet republics in the former Russian Empire, the USSR quickly became a totalitarian state under Communist rule. After the defeat of Nazi Germany in World War II, the competing geopolitical ambitions of the USSR and its former Western allies led to the Cold War. In 1991, most of the constituent republics declared their independence, and the USSR was officially dissolved. Moscow was the capital.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.Union of Soviet Socialist Republics n (Placename) the official name of the former Soviet Union Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Un?ion of So?viet So?cialist Repub?lics n. a former federal union of 15 constituent republics, in E Europe and N Asia, comprising the larger part of the earlier Russian Empire: dissolved in December 1991. 8,650,069 sq. mi. (22,402,200 sq. km). Cap.: Moscow. Also called Soviet Union. Abbr.: U.S.S.R., USSR Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.