tetrahedron Meaning, Definition & Usage

  1. noun any polyhedron having four plane faces

WordNet

Tet`ra*he"dron noun
Etymology
Tetra- + Gr. seat, base, fr. to sit.
Definitions
  1. (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.

Webster 1913