What is "polytetrahedron"

n. 1 A uniform convex polychoron made up of 600 tetrahedral cells; a hexacosichoron. 2 A connected set of regular tetrahedra, the 3-dimensional analogue of a polyiamond.

Polytetrahedron is a term used for three distinct types of objects, all based on the tetrahedron:

• A uniform convex 4-polytope made up of 600 tetrahedral cells. It is more commonly known as a 600-cell or hexacosichoron. Other derivative 4-polytope are identified as polytetrahedra, where a qualifying prefix such as rectified or truncated is used.
• A connected set of regular tetrahedra, the 3-dimensional analogue of a polyiamond. Polytetrahedra and polyiamonds are related as polycubes are related to polyominoes.
• In origami, a polypolyhedron is "a compound of multiple linked polyhedral skeletons with uniform nonintersecting edges" 1. There exist two topologically distinct polytetrahedra, each made up of four intersecting triangles.