The nonagon, also known as an enneagon, is a 9-sided polygon. Although the term "enneagon" is perhaps preferable (since it uses the Greek prefix and suffix instead of the mixed Roman/Greek nonagon), the term "nonagon," which is simpler to spell and pronounce, is used in this work. Several special types of nonagons are illustrated above. In particular, a nonagon with vertices equally spaced around a circle and with all sides the same length is a regular polygon known as a regular nonagon.