What does rhombohedron mean?
A rhombohedron is a three-dimensional polyhedron made from six congruent rhombic faces. Because every face is a rhombus—a parallelogram with equal sides—a rhombohedron belongs to the broader class of parallelepipeds, but it has a more symmetrical and recognizable appearance. Its opposite faces are parallel, while the angles between its edges may be oblique; the cube is a special case in which the rhombic faces are squares. The term is especially useful in crystallography and mineralogy, where it describes the characteristic external shape and symmetry of crystals. It also appears in discussions of crystalline materials and unit cells, where the geometry of a rhombohedron can determine properties such as symmetry, cleavage, and diffraction. The word should not be confused with a rhomboid, which is a flat, two-dimensional parallelogram. For general readers, rhombohedron offers a precise term for a familiar but often overlooked three-dimensional shape.
nounA three-dimensional polyhedron with six congruent rhombus-shaped faces, each pair of opposite faces parallel. It is a special type of parallelepiped and includes the cube as a special case.
- A three-dimensional polyhedron whose six congruent faces are rhombi, with opposite faces parallel.
"The crystal's external shape is a rhombohedron, with six matching rhombic faces."
"The mineral crystallizes as a rhombohedron bounded by six sparkling faces."
"In the model, each unit cell is represented by a rhombohedron rather than a cube."
The standard plural is rhombohedra.
"Several small rhombohedra occur throughout the mineral sample."
Six rhombic faces meet in a rhombohedron—the three-dimensional relative of a rhombus.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does rhombohedron come from?
The word is a Neo-Latin formation combining Greek rhómbos, meaning a rhombus or lozenge-shaped figure, with Greek hédra, meaning a base, seat, or side. The second element also appears in the established combining form -hedron, used in the names of polyhedra such as tetrahedron and hexahedron. Its development followed the Greek naming tradition for geometric solids and later became firmly established in mathematical and crystallographic writing.
Related word forms
How rhombohedron is actually used
This is a specialized formal term used in geometry, mineralogy, crystallography, and materials science. It is uncommon in everyday speech and is normally used in technical descriptions of solid forms, crystal structures, and lattice geometry.
Easily confused with rhombohedron
A rhomboid is a two-dimensional parallelogram with opposite sides equal, whereas a rhombohedron is a three-dimensional solid with six rhombic faces.