Former country on the Balkan Peninsula. In addition to Serbia and Montenegro, Republic of Macedonia, Bosnia-Herzegovina, Slovenia, and Croatia were also part of the Yugoslav Federation prior to the 1990s, noun_ a former country of southeastern Europe bordering the Adriatic Sea; formed in 1918 and named Yugoslavia in 1929; controlled by Marshal Tito as a communist state until his death in 1980, a mountainous republic in southeastern Europe bordering on the Adriatic Sea; formed from two of the six republics that made up Yugoslavia until 1992; Serbia and Montenegro were known as the Federal Republic of Yugoslavia until 2003 when they adopted the name of the Union of Serbia and Montenegro