What is the common name for a polygon with 8 sides?

A polygon with 8 sides is known as an octagon. The term "octagon" is derived from the Greek words "okto," meaning eight, and "gonia," meaning angle. Thus, an octagon has eight angles and eight corresponding sides. In geometry, this shape is widely recognized, especially in contexts such as stop signs, which are typically octagonal.

The other options represent polygons with different numbers of sides: a heptagon has seven sides, a nonagon has nine sides, and a decagon has ten sides. Each of these names is also derived from Greek numerical prefixes reflecting the count of their sides, further highlighting the specificity of polygon naming conventions.