n. [ Gr. &unr_; twenty + &unr_;, combining form of &unr_; four + &unr_; seat, base. ] (Crystallog.) A twenty-four-sided solid; a tetragonal trisoctahedron or trapezohedron. [ 1913 Webster ]
n. [ Tetra- + Gr. &unr_; seat, base, fr. &unr_; to sit. ] (Geom.) A solid figure inclosed or bounded by four triangles. [ 1913 Webster ]
☞ In crystallography, the regular tetrahedron is regarded as the hemihedral form of the regular octahedron. [ 1913 Webster ]
Regular tetrahedron (Geom.),