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Polygon names
By Jonty Young on Friday, October 1, 1999 - 09:44 am:

Dear NRICH Maths,
I wanted to know a few things for some maths we've been doing at school.

* What is a 9 sided shape called?
* What is a 10sided shape called?
* What is an 11 sided shape called?
* What is a 12 sided shape called?

I think your site is great. My maths teacher recommended it to me!

Thanks!

Bye!!!
Jonty Young, Age 11
Oxfordshire.

By Alex Barnard (Agb21) on Friday, October 1, 1999 - 12:07 pm:


9-sided is a nonagon
10-sided is a decagon
11-sided is an undecagon
12-sided is a dodecagon

Glad to hear you like the site. If you want to know any more things about polygons do let us know.
AlexB.

An earlier thread on the same subject (and another answer!):
By Victoria Eves on May 4, 1998:

At school at the moment we are studying polygons, but does anyone know the name of an eleven sided polygon, as I don't think that there is a name for them, but would be interested to know if there is one.

Also, do you know any other names for different amounts of sides of a polygon e.g. 26 sides etc. How high do the proper names go up?

From Victoria Eves

By Gareth McCaughan on May 6, 1998:

An eleven-sided polygon is called a hendecagon. (But not very often.)

In theory, there are probably as many `proper' names for polygons as there are numbers nameable using classical Greek. In practice, though, you'd write `26-gon' or whatever.

I think my dictionary (that's an ordinary English dictionary, not a specialist one covering mathematics) goes as far as 12 (dodecagon) and no further. I think a 13-gon could be called a `triskaidecagon' if you really wanted; I'm not sure about larger numbers.