In geometry, the tridiminished icosahedron is one of the Johnson solids (J₆₃). The name refers to one way of constructing it, by removing three pentagonal pyramids (J₂) from a regular icosahedron, which replaces three sets of five triangular faces from the icosahedron with three mutually adjacent pentagonal faces.

A Johnson solid is one of 92 strictly convex polyhedra that is composed of regular polygon faces but are not uniform polyhedra (that is, they are not Platonic solids, Archimedean solids, prisms, or antiprisms). They were named by Norman Johnson, who first listed these polyhedra in 1966.^[1]

The tridiminished icosahedron is the vertex figure of the snub 24-cell, a uniform 4-polytope (4-dimensional polytope).

• Diminished icosahedron (J₁₁)
• Metabidiminished icosahedron (J₆₂)