last updated: 2005-10-30

The enneagon is the nine-sided polygon, also known as an nonagon.
In the word enneagon both the prefix and the suffix are Greek, the nonagan is a mix of Roman and Greek. Therefore we prefer the enneagon name.

The regular enneagon is the regular polygon with nine sides.

The regular enneagon cannot be constructed using the classical Greek rules of geometric construction, but it can be done using a Neusis construction.