octahedron

n. three-dimensional figure with eight plane surfaces

An octahedron (plural: octahedra) is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each . The octahedron's symmetry group is Oh, of order 48. This group's subgroups include D3d (order 12), the symmetry group of a triangular antiprism; D4h (order 16), the symmetry group of a square bipyramid; and Td (order 24), the symmetry group of a rectified tetrahedron. These symmetries can be emphasized by different decorations of the faces.
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(n.)
A solid bounded by eight faces. The regular octahedron is contained by eight equal equilateral triangles.
  

Noun
1. any polyhedron having eight plane faces
(hypernym) polyhedron