What is "regular icosahedron"

Icosahedron \I`co*sa*he"dron\, n. [Gr. ?; ? twenty + ? seat, base, fr. ? to sit.] (Geom.) A solid bounded by twenty sides or faces.

Regular icosahedron, one of the five regular polyhedrons, bounded by twenty equilateral triangules. Five triangles meet to form each solid angle of the polyhedron.

n. an icosahedron with twenty equilateral triangles as faces

In geometry, a regular icosahedron ( or ) is a convex polyhedron with 20 faces, 30 edges and 12 vertices. It is one of the five Platonic solids.

It has five equilateral triangular faces meeting at each vertex. It is represented by its Schläfli symbol {3,5}, or sometimes by its vertex figure as 3.3.3.3.3 or 3. It is the dual of the dodecahedron, which is represented by {5,3}, having three pentagonal faces around each vertex.

A regular icosahedron is a gyroelongated pentagonal bipyramid and a biaugmented pentagonal antiprism in any of six orientations.

The name comes . The plural can be either "icosahedrons" or "icosahedra" .