What is a regular polygon with 24 sides called?

A regular polygon with 24 sides is called an icositetragon.

The name combines Greek-derived numerical elements: “icosi” refers to twenty and “tetra” to four, giving twenty-four sides. It is also commonly described simply as a 24-gon, while icosikaitetragon is an alternative form of the name.

In a regular icositetragon, all 24 sides and all 24 interior angles are equal. Each interior angle measures 165 degrees, because the interior-angle sum is (24 − 2) × 180 = 3,960 degrees. Each exterior angle is therefore 15 degrees, and the polygon has rotational symmetry through one twenty-fourth of a full turn.

The distractors name different polygons: an icosagon has 20 sides, a triacontagon has 30, and a dodecagon has 12. The 24-gon is also mathematically notable because 24 = 2³ × 3, so a regular version can be constructed with compass and straightedge; it can be made by truncating a regular dodecagon.