Tetrahedron (noun)

1. A three-dimensional geometric shape with four triangular faces and four vertices.
2. A solid figure in which each of its faces is a triangle and its solid angles are all equal to four right angles.

Origin:

From greek tetra- ("four") + -hedron ("seat, base, face").

Examples:

1. The tetrahedron is one of the five Platonic solids.
2. The tetrahedron has four faces that are all equilateral triangles.
3. The molecule of methane is composed of one carbon atom and four hydrogen atoms arranged in a tetrahedron.
4. In the study of geometry, the tetrahedron is considered a regular polyhedron.
5. The tetrahedron is often used in computer graphics to represent 3D objects.