tetrahedron: see polyhedronpolyhedron
, 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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A polygon with four plane surfaces.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
(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 .
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
An isometric crystal form in cubic crystals, in the shape of a four-faced polyhedron, each face of which is a triangle.
A four-sided polyhedron.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
1. a solid figure having four plane faces. A regular tetrahedron has faces that are equilateral triangles
2. any object shaped like a tetrahedron
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005