from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A polyhedron composed of two parallel copies of some particular polygon, connected by an alternating band of triangles.
from The Century Dictionary and Cyclopedia
- n. An auxiliary prism; part of a compound prism placed with its refractive edge in a reversed position.
anti- + prism (Wiktionary)
But math-crazy Lovecraft would have known that a trapezohedron is an "antiprism."