icosahedral

• icosahedric (much less common[1])

icosa- +‎ -hedral

icosahedral (not comparable)

1. Of, relating to, or having the shape of an icosahedron.
   • 1966, Norman W. Johnson, “Convex Polyhedra with Regular Faces”, in Canadian Journal of Mathematics, volume XVIII, number I, Toronto: University of Toronto Press, page 181:

     Of the convex polyhedra with regular faces, the only ones that have tetrahedral, octahedral, or icosahedral symmetry are the Platonic and Archimedean solids.

• icosahedron

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