Is it ensure, insure, or assure?
Plural polyhedrons or polyhedra
A three-dimensional geometric figure whose sides are polygons. A tetrahedron, for example, is a polyhedron having four triangular sides. ◇ A regular polyhedron is a polyhedron whose faces are all congruent regular polygons. The regular tetrahedron (pyramid), hexahedron (cube), octahedron, dodecahedron, and icosahedron are the five regular polyhedrons. Regular polyhedrons are a type of Archimedean solid.