Source : Webster's Revised Unabridged Dictionary (1913)

Tetrahedral \Tet`ra*he"dral\, a. [See {Tetrahedron}.]
   1. Having, or composed of, four sides.

   2. (Crystallog.)
      (a) Having the form of the regular tetrahedron.
      (b) Pertaining or related to a tetrahedron, or to the
          system of hemihedral forms to which the tetrahedron
          belongs.

   {Tetrahedral angle} (Geom.), a solid angle bounded or
      inclosed by four plane angles.