Geometry and Trigonometry

Plane Geometry

What are the names given to regular polygons?

Polygons are classified according to the number of sides they have. A polygon with n sides is called an n-gon. The following lists some of the names of polygons, depending on the number of sides. It is also possible to substitute “n-gon,” when the name is not known (for example 14-gon or 20-gon).

Sides Polygon Name
3 trigon or triangle
4 quadrilateral or tetragon
5 pentagon
6 hexagon
7 heptagon
8 octagon
9 nonagon or enneagon
10 decagon
11 hendecagon or undecagon (even less frequently as unidecagon)
12 dodecagon
13 tridecagon or triskaidecagon
14 tetradecagon or tetrakaidecagon
15 pentadecagon or pentakaidecagon
16 hexadecagon or hexakaidecagon
17 heptadecagon or heptakaidecagon
18 octadecagon or octakaidecagon
19 enneadecagon or enneakaidecagon
20 icosagon
30 triacontagon
40 tetracontagon
50 pentacontagon
60 hexacontagon
70 heptacontagon
80 octacontagon
90 enneacontagon
100 hectogon or hecatontagon
1,000 chiliagon
10,000 myriagon

Some texts list a two-sided polygon as a “digon,” but this is only meant for theoretical mathematics. If you feel like making up your own name, try constructing some sided polygons. For example, a 46-sided polygon could be called a tetracontakai-hexagon, or a combination of “tetracon-tagon” + “kai” (often used in combining names) + “hexagon.” To shorten such long names, mathematicians often use “n-gon” to simplify matters; thus, 46 would be 46-gon a much easier name to remember and even say.


The parts of a polygon.


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