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Webster 1913 Edition

Tetrahedron

Tetˊra-he′dron

,
Noun.
[
Tetra-
+ Gr. [GREEK] seat, base, fr. [GREEK] to sit.]
(Geom.)
A solid figure inclosed or bounded by four triangles.
☞ In crystallography, the regular tetrahedron is regarded as the hemihedral form of the regular octahedron.
Regular tetrahedron
(Geom.)
,
a solid bounded by four equal equilateral triangles; one of the five regular solids.

Webster 1828 Edition

Tetrahedron

TETRAHE'DRON

,
Noun.
[Gr. four, and side.] In geometry, a figure comprehended under four equilateral and equal triangles; or one of the five regular Platonic bodies of that figure.

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