A nine-sided figure is also known as a nonagon or enneagon. A nonagon has seven letters and an enneagon has eight letters. A nonagon is a polygon with nine sides and nine angles, while an enneagon is a nine-sided figure with nine vertices. Both figures are regular polygons, meaning that all sides and angles are equal. Nonagons and enneagons are often used in architecture and design, as well as in mathematics.