disphenoid

Etymology
From.

Adjective

 * 1)  Of or pertaining to a wedge-shaped crystal form of the tetragonal or orthorhombic system.
 * 2)  Of or pertaining to a crystal form bounded by eight scalene triangles arranged in pairs, constituting a tetragonal scalenohedron.

Noun

 * 1)  A non-regular tetrahedron whose four faces are congruent acute-angled triangles.
 * 2) * 1973,, 3rd Edition, unnumbered page,
 * To make a model of a disphenoid, cut out an acute angled triangle and fold it along the joins of the mid-points of the sides. The disphenoid is said to be rhombic or tetragonal according as the triangle is isosceles or scalene.
 * To make a model of a disphenoid, cut out an acute angled triangle and fold it along the joins of the mid-points of the sides. The disphenoid is said to be rhombic or tetragonal according as the triangle is isosceles or scalene.