Question: a hexahedron which is a pyramid?
Answer: A hexahedron is a polyhedron with six faces. The unique regular hexahedron is the cube. Two hexahedra can be built from regular polygons with equal edge lengths: the equilateral triangular dipyramid and pentagonal pyramid. Rhombohedra are a special class of hexahedron in which opposite faces are congruent rhombi.