A enneahedron (plural: enneahedra) is a polyhedron having nine sides, or faces.
A enneahedron can take a surprising number of different basic forms, or topologies. The most familiar are the octagonal pyramid, and the heptagonal prism. Others from the Johnson solids include the elongated square pyramid, gyroelongated square pyramid, triaugmented triangular prism, and the tridiminished icosahedron. No enneahedra are regular.
There are 2606 topologically distinct convex enneahedra, excluding mirror images.[1]