An 11-sided shape is called a hendecagon. The name is derived from the Greek words "hendeka," which means 11, and "gon," which means corner.
An 11-sided shape may also be called an undecagon or unidecagon, which is partly derived from the Latin word undecima, which means 11. However, most people prefer to use the word hendecagon because it consists of purely Greek words as opposed to a mix of Latin and Greek. Common properties of a regular hendecagon include 33-degree exterior angles and 147-degree internal angles. A real life example of a hendecagon is the rim of the U.S. Susan B. Anthony dollar coin.