1. an icosahedron with twenty equilateral triangles as faces;
The Collaborative International Dictionary of English v.0.48:
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.
WordNet (r) 3.0 (2006):
n 1: an icosahedron with twenty equilateral triangles as faces