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.