1) Polyhedron 
• (a.) Having twenty equal sides or faces.
Many sided; a type of virus which does not possess an envelope and has a crystalline appearance; naked virus.
I`co·sa·he'dral adjective [ See Icosahedron .] (Geom.) Having twenty equal sides or faces. 
Type: Term Pronunciation: ī′kō-să-hē′drăl Definitions: 1. Having 20 equilateral triangular surfaces and 12 vertices, as do most viruses with cubic symmetry.
[adj] - of or relating to an icosahedron
three-dimensional, 20-sided structure with 12 vertices
adjective of or relating to an icosahedron