from The Century Dictionary and Cyclopedia
- In mathematics, a four-dimensional body bounded by 5 tetrahedra.
Sorry, no etymologies found.
Any five points, not all in one three-space, may be regarded as the vertices of a pentahedroid.
The simplest case of a hyperpyramid is a figure called a pentahedroid.
These five points, taken four at a time, give us five tetrahedrons and the pentahedroid may be taken in five different ways as a hyperpyramid.
The pentahedroid is formed by turning these toward one another until they are brought completely together again.