What does pentahedral mean?
Pentahedral is the standard adjective for something with five faces. It is especially useful in geometry and crystallography when describing a solid, crystal, or symmetry, and in chemistry when describing a molecular arrangement around a central atom. Unlike the more familiar word five-sided, pentahedral gives the description a technical, classificatory quality. A pentahedron is a polyhedron with five faces, but the term does not imply that the faces are regular or that all the faces have the same shape. Pentahedral geometry is also related to, but not restricted to, the trigonal bipyramid, one of the common ways five neighboring atoms or ligands can be arranged around a central atom. The word is consequently precise and useful whenever naming the number of faces is more appropriate than describing their individual shapes.
adjectiveHaving five faces. The term is used chiefly in geometry, chemistry, and crystallography to describe five-faced forms or arrangements.
- Having five faces, especially in geometry, crystallography, or molecular structure.
"The mineral's crystals display a distinctive pentahedral structure."
"The compound adopts a roughly pentahedral coordination around its central metal atom."
"The museum's display case was designed to emphasize the sculpture's pentahedral geometry."
A shape with five faces has plenty of character, but one popular five-faced shape is famously not a regular polyhedron: the triangular bipyramid.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does pentahedral come from?
Pentahedral was formed within the English vocabulary of geometry from the combining form penta-, meaning 'five', and the suffix -hedral, meaning 'having a specified number of faces.' The latter continues Greek hedra, 'face' or 'base', through the related word polyhedron and its derivatives. The same Greek numerical element underlies words such as pentagon and pentathlon.
Related word forms
How pentahedral is actually used
This is primarily a technical term. In chemistry, it describes an arrangement associated with coordination number five, though the precise geometry may be trigonal bipyramidal or square pyramidal.
Easily confused with pentahedral
Pentahedral means having five faces, whereas pentagonal means having five sides or angles.