18
These are very hard to spell but here you go: 17 faces: septadecahedron 18 faces: octadecahedron 19 faces: nonadecahedron 20 faces: icosahedron 21 faces: unicosahedron 22 faces: dicosahedron 29 faces: nonicosahedron 30 faces: tricontahedron
Names of 3D shapes 1 face: sphere 4 faces: tetrahedron/triangle based pyramid 5 faces: pentahedron/square based pyramid 6 faces: hexahedron (sexahedron)/cube/cuboid 7 faces: septahedron 8 faces: octahedron 9 faces: nonahedron 10 faces: decahedron 11 faces: undecahedron 12 faces: dodecahedron 13 faces: tridecahedron 14 faces: tetradecahedron 15 faces: pentadecahedron 16 faces: hexadecahedron (sexadecahedron) 17 faces: septadecahedron 18 faces: octadecahedron 19 faces: nonadecahedron 20 faces: icosahedron 21 faces: unicosahedron 22 faces: dicosahedron ... 29 faces: nonicosahedron 30 faces: tricontahedron 90 faces: ennacontahedron