# Definition:Icosahedron

## Definition

An icosahedron is a polyhedron which has $20$ faces.

### Regular Icosahedron

A regular icosahedron is an icosahedron whose $20$ faces are all congruent equilateral triangles.

### Truncated Icosahedron

A truncated icosahedron is an icosahedron whose $12$ vertices are truncated such that one third of each edge is cut off at each of both ends.

## Also see

• Results about icosahedra can be found here.

## Linguistic Note

The word icosahedron derives from the Classical Greek εἰκοσάεδρον:

eíkosi (εἴκοσι), meaning twenty
hedron (a form of ἕδρα), meaning base or seat.

The technically correct plural of icosahedron is icosahedra, but the word icosahedrons can often be found.