# tetrahedron

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## tetrahedron:

see polyhedron**polyhedron**

, closed solid bounded by plane faces; each face of a polyhedron is a polygon. A cube is a polyhedron bounded by six polygons (in this case squares) meeting at right angles.

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## Tetrahedron

A polygon with four plane surfaces.

## Tetrahedron

(or triangular pyramid), a polyhedron with four triangular faces, six edges, and four vertices. At each vertex three edges intersect. The regular tetrahedron (Figure 1) is one

of the five regular polyhedrons. If *a* is the length of an edge of a regular tetrahedron, the volume of the tetrahedron is .

## tetrahedron

[‚te·trə′hē·drən] (crystallography)

An isometric crystal form in cubic crystals, in the shape of a four-faced polyhedron, each face of which is a triangle.

(mathematics)

A four-sided polyhedron.

## tetrahedron

A device to indicate wind direction, and, in turn, landing direction. It is tetrahedronshaped—four triangular sides. This device is generally located at uncontrolled airports. The small end of a tetrahedron points in the direction of landing. At controlled airports, the tetrahedron should be disregarded because tower instructions supercede the indicator. On approach charts, a tetrahedron is shown as.

## tetrahedron

**1.**a solid figure having four plane faces. A

**regular tetrahedron**has faces that are equilateral triangles

**2.**any object shaped like a tetrahedron