Twentysided

Twentysided is an adjective used to describe an object that has twenty sides or faces. In geometry, the term can refer to any twenty-faced polyhedron, with the most notable example being the regular icosahedron.

The regular twenty-faced polyhedron, the icosahedron, has 20 equilateral triangular faces, 30 edges, and 12 vertices. It is one of the five Platonic solids and is the geometric dual of the regular dodecahedron (which has 12 pentagonal faces). While the icosahedron is a highly symmetric shape, many twenty-faced polyhedra that are not regular also exist and are studied in geometry and modeling.

In popular culture and gaming, twenty-sided shapes are most widely encountered as the twenty-sided die, or d20. The d20 is a common component of tabletop role-playing games such as Dungeons & Dragons, where each face represents a possible result from 1 to 20. On a fair d20, each face has an equal probability of landing face up. Some dice are numbered so that opposite faces sum to 21, a convention used by many manufacturers, though the arrangement does not affect the die’s fairness.

Beyond gaming, twenty-faced polyhedra appear in mathematical modeling, art, and design, where their geometry can provide interesting symmetries and tiling properties. The term twentysided thus encompasses both the geometric object and its descriptive use in various contexts.