Recent Examples on the WebThey are defined by symmetry, and the Greeks knew that there were only five possibilities meeting the criteria: the tetrahedron, cube, octahedron, dodecahedron and icosahedron. Eugenia Cheng, WSJ, 10 Aug. 2017 Diamonds, which form eight-sided crystals called octahedrons, can be billions of years old, Dr. Harlow said. C. Claiborne Ray, New York Times, 12 June 2017