A regular one has internal angles of 140 degrees

• Shape of every Baha'i temple
• Canon agonises somewhat to reveal figure
• Nine-sider
• Figure a small number continue to badger
• It has nine angles and nine sides
• Odd-shaped figure
• A nine-sided polygon

Wikipedia Word definitions in Wikipedia
In geometry , a nonagon (or enneagon ) is a nine-sided polygon or 9-gon. The name "nonagon" is a prefix hybrid formation, from Latin ( nonus , "ninth" + gonon ), used equivalently, attested already in the 16th century in French nonogone and in English from ...

WordNet Word definitions in WordNet
n. a nine-sided polygon

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Nonagon \Non"a*gon\, n. [L. nonus ninth + Gr. ? angle.] (Math.) A plane figure or polygon having nine sides and nine angles.