Noun | 1. | battle of Tannenberg - a battle in World War I (1914); decisive German victory over the Russians First World War, Great War, War to End War, World War 1, World War I - a war between the allies (Russia, France, British Empire, Italy, United States, Japan, Rumania, Serbia, Belgium, Greece, Portugal, Montenegro) and the Central Powers (Germany, Austria-Hungary, Turkey, Bulgaria) from 1914 to 1918 Poland, Polska, Republic of Poland - a republic in central Europe; the invasion of Poland by Germany in 1939 started World War II |