NAMING POLYGONS
Naming a polygon by its number of sides requires that we know the appropriate Greek prefixes along with some rules for their use.
3
 = tri
4
 = tetra
5
 = penta
6
 = hexa or sexa
7
 = hepta
8
 = octa
9
 = nona or ennea
10
 = deca
11
 = undeca or hendeca
12
 = dodeca
13
 = triskaideca
14
 = tetradeca
15
 = pentadeca
16
 = hexadeca
17
 = heptadeca
18
 = octadeca
19
 = enneadeca
20
 = icosa
For polygons with 3 through 20 sides, simply add "gon" to the prefixes at the left (although a trigon is more commonly called a triangle and a tetragon, a quadrilateral!).

For more than 20 sides, we "construct" the name by using so-called combining prefixes:

Tens Digit
20
 = icosi
30
 = triaconta
40
 = tetraconta
50
 = pentaconta
60
 = hexaconta
70
 = heptaconta
80
 = octaconta
90
 = enneaconta

Ones Digit
1
 = hena
2
 = di
3
 = tri
4
 = tetra
5
 = penta
6
 = hexa
7
 = hepta
8
 = octa
9
 = ennea
3 - 99 SIDES
To "construct" a name, we start with the prefix for the tens digit, follow it by "kai" (the Greek word for "and"), then follow it with the prefix for the units digit, and finally add "gon."

Example: A 35-sided polygon is called a "triacontakaipentagon."

30

and

5

gon

triaconta

kai

penta

gon

100 - 999 SIDES
For numbers from 100 to 999, we need one more combining prefix and another rule.

To "construct" the name, we start with the prefix for the hundreds digit taken from the "Ones Digit" table above, follow it by "hecta," then proceed as before.

Example: A 672-sided polygon is called a "hexahectaheptacontakaidigon."

100
=
 hecta

600

70

and

2

gon

hexa + hecta

heptaconta

kai

di

gon
Now you try some. When you think have the name, click on the ANSWER button to check.

83 sides

257 sides

999 sides