Unvigintagonal

Unvigintagonal refers to a polygon with twenty-one sides. The term is derived from Latin, with "un" meaning one, "viginti" meaning twenty, and "agonal" referring to angles or sides. Therefore, an unvigintagonal polygon has twenty-one angles and twenty-one sides.

In geometry, polygons are classified by the number of their sides. Common polygons include triangles (3 sides), quadrilaterals (4 sides), pentagons (5 sides), and so on. The prefix "unviginti-" specifically denotes the quantity twenty-one.

A regular unvigintagonal polygon has all sides of equal length and all interior angles equal. The measure of each interior angle in a regular unvigintagonal polygon can be calculated using the formula (n-2) * 180 / n, where n is the number of sides. For n=21, this yields (21-2) * 180 / 21 = 19 * 180 / 21 = 3420 / 21 = 162.857 degrees.

The term "unvigintagonal" is not as commonly used as terms for polygons with fewer sides, such as pentagon or hexagon. However, it adheres to the systematic naming convention for polygons based on their side count.