Definition:Nonagon

Definition

A nonagon is a polygon with exactly $9$ sides.

Regular Nonagon

A regular nonagon is a nonagon which is both equilateral and equiangular.

That is, a regular polygon with $9$ sides.

That is, a nonagon in which all the sides are the same length, and all the vertices have the same angle:

Also known as

A nonagon can also be referred to as an enneagon.

Linguistic Note

The word nonagon is a hybrid word from the Latin nonus, meaning ninth, and gon, deriving from the Greek for corner.

The arguably more correct (but less common) word enneagon is purely Greek in derivation, the first part coming from ennea, meaning nine.

Sources

• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): nonagon (enneagon)
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): nonagon (enneagon)
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): enneagon
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): nonagon
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): polygon
• 2021: Richard Earl and James Nicholson: The Concise Oxford Dictionary of Mathematics (6th ed.) ... (previous) ... (next): polygon