Hebesphenomegacorona
We’re into one of the more arcane areas of three-dimensional geometry. This figure is a polyhedron, a solid figure with flat faces. It was given this name in 1969 by Viktor Zalgaller, in an article in which he proved an abstruse result about a set of irregular polyhedra called the Johnson solids. These polyhedra are named after N W Johnson, who had suggested three years earlier that there were just 92 of them. Mr Zalgaller proved this was so and gave each of the 92 polyhedra a unique name. Hebesphenomegacorona can be split into four parts as hebe (from the Latin word for “blunt”), spheno (from the Greek for “wedge”), mega (Greek, “great”), and corona (Latin, “crown”), so making a “large, blunt, wedge-shaped crown”. He came up with many splendid names for other members of the set, like square dipyramid, pentagonal orthocupolarontunda, gyrobifastigium, metabidiminished rhombicosidododecahedron, snub disphenoid, gyroelongated disphenocingulum, elongated pentagonal gyrocupolarotunda, and triangular orthobicupola. There's heavy odds against you finding any of them in even the largest dictionaries.