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A solid with six quadrilateral faces. A regular hexahedron is a cube.

The Greeks first used the terms Octahedron and Icosahedron to describe regular 8 and 20 side polyhedra. There was already a name for the cube, so the term Hexahedron was not used. However, we can distinguish between regular and irregular forms of these solids, so the term Hexahedron now finds some use. Note that there are some 6 sided solids that are not hexahedra - such as the pentagonal pyramid.