Nonagon or Enneagon?

Date: 02/06/2003 at 11:21:05
From: David
Subject: 9-sided polygons

I noticed in Conway's post 

   Naming Polygons
   http://mathforum.org/library/drmath/view/57666.html 

that "nonagon" is not the correct name for a 9-sided polygon.  Every 
textbook I've referred to uses it, however. Is "enneagon" really the 
correct name? If so, why do all of the textbooks have it wrong?

Date: 02/06/2003 at 12:10:01
From: Doctor Peterson
Subject: Re: 9-sided polygons

Hi, David.

Dictionaries, too, usually list "nonagon" and "undecagon" rather than 
Conway's preferred "enneagon" and "hendecagon," if they list either. 
That's because they are "descriptive," telling how people actually 
use words, rather than being "prescriptive," telling how they would 
use words if they were intelligent. ;-)

The fact is that English has never been as consistent as people like 
Dr. Conway and me, who enjoy the study of etymology, wish it were. I 
note that Merriam-Webster explains the origin of "nonagon" this way:

    Latin nonus ninth + English -gon 

This avoids the fact that "-gon" ultimately comes from Greek, making 
this a sort of hybrid that irritates purists; but it is probably 
realistic to recognize that words like this are invented in English, 
and are thought of as made from English roots, not from Latin and 
Greek. Since people are far more familiar with "nona-" than with 
"ennea-", it is natural that the former seems obviously right to all 
but the most knowledgeable.

So keep using "nonagon"; in practice there's nothing wrong with it. 
But if you like idealistic campaigns, you may get on the "enneagon" 
bandwagon with us; there's plenty of room aboard!

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/