Geometric solid all of whose faces are identical regular polygons and all of whose angles are equal. There are only five such polyhedrons. The cube is constructed from the square, the dodecahedron from the regular pentagon, and the tetrahedron, octahedron, and icosahedron (with 20 faces) from the equilateral triangle. They are known as the Platonic solids because of Plato's attempt to relate each to one of the five elements that he believed formed the world.

Learn more about Platonic solid with a free trial on Britannica.com.