What is the wedge-shaped stone at the top of an arch that locks the other stones in place?

Which Konami arcade game, known as DDR, has players stomping on arrow panels in time with music? What does an archer draw back to launch an arrow? Which Nazi architect and armaments minister wrote the memoir "Inside the Third Reich"? Which Paris school gave its name to an ornate architectural style, though it dropped architecture teaching in 1968? Which piano virtuoso and ardent Polish patriot served as Poland's prime minister in 1919? Joe Louis Arena, the site of the 1980 Republican National Convention, is in which city? The "Arkansas toothpick" is a large type of what? At which village was the armistice ending the fighting of the Korean War signed in July 1953?