A five-sided figure is commonly known as a pentagon. However, there are several other synonyms that can be used for this shape, depending on the specific properties and measurements of the sides and angles. For instance, if all sides of the pentagon are equal in length, it is called a regular pentagon. A concave pentagon has at least one internal angle greater than 180 degrees and is sometimes referred to as a star pentagon. A dodecagon is a 12-sided figure and can be seen as a doubled version of a pentagon. Lastly, a nonagon is a nine-sided figure, which is obtained by removing one of the five sides of the pentagon and adding four more.