An octahedron is a polyhedron with eight faces and twelve sides. With a regular octahedron each face is an equilateral triangle.
It looks like a cube shaped more like a 3d diamond as a 2d diamond looks like an elongated square. Two pyramids with their bases together.
One of the 5 platonic solids.

4 faces (and edges) meet at every vertex.

So the dual polyhedron is the cube.

Oc`ta*he"dron (?), n. [Gr., fr. eight-side; (for eight) + seat, base, from to sit.] Geom.

A solid bounded by eight faces. The regular octahedron is contained by eight equal equilateral triangles.


© Webster 1913.

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