**Geometric Nomenclature 102**
At the most basic level, the system for naming

polyhedra is nearly

identical to that for

naming polygons. Consequently much of this node is a

cut and paste effort from

Geometric Nomenclature 101. Never fear, polyhedra are inherently more

complex than the humble

polygon. Thus, the naming of more

obscure polyhedra can be an interesting affair.

The -hedron suffix of

polyhedron means "seat", but by considering the less literal translational of "face" we can see why objects of

*many faces* are indeed called polyhedrons.

**Basic prefixes**
Polyhedral (and polygonal) prefixes are of Greek

origin. This explains why the prefix relating to

seven is

*hepta-* rather than

*septa-*, as 's' in English corresponds to 'h' in Greek.

**Units**
**1** hena-
**2** di-
**3** tri-
**4** tetra
**5** penta-
**6** hexa-
**7** hepta-
**8** octa-
**9** ennea-
**10** decahedron
**11** hendecahedron,

undecahedron
**12** dodecahedron
**Teens**
**13** trisdecahedron
**14** tetradecahedron
**15** pentadecahedron
**16** hexadecahedron
**17** heptadecahedron
**18** octadecahedron
**19** enneadecahedron
**Tens**
**10** decahedron
**20** icosahedron
icosi +

*unit prefix*
**30** tricontahedron
triconta +

*unit prefix*
**40** tetracontahedron
tetraconta +

*unit prefix*
**50** pentacontahedron
pentaconta +

*unit prefix*
**60** hexacontahedron
hexaconta +

*unit prefix*
**70** heptacontahedron
heptaconta +

*unit prefix*
**80** octacontahedron
octaconta +

*unit prefix*
**90** enneacontahedron
enneaconta +

*unit prefix*
**100** hectohedron
hecta +

*tens prefix* +

*unit prefix*
**1000** chiliahedron
**10000** myriahedron
**Not-so-basic prefixes**
Often a polygonal term is placed in front of the polyhedron name to indicate

face shape. For example, a

*pentagonal tetracontahedron* is a polyhedron of 40 faces, each with 5 sides. Beyond indicating the number of sides on each face, these face descriptors may refer to the

shape of each face.

Rhombic polyhedron and

trapezoidal polyhedron for instance.

You might also see the term

*-kis* at the end of a (numerical) face descriptor. This indicates that the polyhedron in question has been formed by taking a simpler polyhedron and dividing each face into several

isosceles triangles.

For example. an

*icositetrahedon* (24 sides) could be formed by taking a

*cube* and dividing each face into 4 triangles, resulting in a

*tetrakis cube*. In this case, the tetra- is redundant so this shape could just be called a

*kis cube*.