The name is derived from Greek roots, and so the name, not surprisingly, is "tetrahedron".
Tetrahedron. http://en.wikipedia.org/wiki/Tetrahedron
tetrahedron
A tetrahedron.
A triangular pyramid.
A tetrahedron.
tetrahedron
A tetrahedron.
Tetrahedron
A tetrahedron.
a tetrahedron
A triangle-based pyramid.