English

An elongated triangular bipyramid, an example of an enneahedron

A heptagonal prism, another enneahedron

Noun

enneahedron ‎(plural enneahedra)

1. (geometry) A polyhedron with nine faces.
   • 1968, Design, Issues 229-234, unnumbered page,

     The enneahedron is a simple all-space filler discovered by myself, based on the cubic antiprism, again omitted by Wood.

   • 1996, Michael O'Keeffe, Bruce G. Hyde, Crystal Structures, Number 1: Patterns & Symmetry, page 350,

     This is based on a packing of 36-vertex icosahedra [5¹².6⁸] and enneahedra (4³.5⁶].

   • 2015, Claudi Alsina, Roger B. Nelsen, A Mathematical Space Odyssey: Solid Geometry in the 21st Century, page 191,

     In Figure 9.10.3 we see a projection of the skeleton of an enneahedron (a solid with nine faces). All the faces of this enneahedron are quadrilaterals.

Related terms

• enneagon
• enneahedral