In geometry, an icosagon is a twenty-sided polygon or 20-gon.

A regular square, pentagon, and icosagon can completely fill a plane vertex.

As a golygonal path, the swastika is considered to be an irregular icosagon.

The college also has a central quad, although it is actually an irregular icosagon, a setting for the college's musical events and formal ball.

These two forms are duals of each other and have half the symmetry order of the regular icosagon.

The regular icosagon has Dih symmetry, order 40.

Geometrically, the swastika can be regarded as an irregular icosagon or 20-sided polygon.

As a truncated icosagon, it can be constructed by an edge-bisection of a regular icosagon.

The regular icosagon is the Petrie polygon for a number of higher-dimensional polytopes, shown in orthogonal projections in Coxeter planes:

These 10 symmetries can be seen in 16 distinct symmetries on the icosagon, a larger number because the lines of reflections can either pass through vertices or edges.

The highest symmetry irregular icosagons are d20, a isogonal icosagon constructed by ten mirrors which can alternate long and short edges, and p20, an isotoxal icosagon, constructed with equal edge lengths, but vertices alternating two different internal angles.

In geometry, an icosagon is a twenty-sided polygon or 20-gon.