Wordnet 3.0
NOUN (1)
1.
any polyhedron having twenty plane 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.
[1913 Webster]
Regular icosahedron, one of the five regular polyhedrons,
bounded by twenty equilateral triangules. Five triangles
meet to form each solid angle of the polyhedron.
[1913 Webster]
WordNet (r) 3.0 (2006):
icosahedron
n 1: any polyhedron having twenty plane faces