A polyhedron with 20 faces is called an icosahedron.
Octohedron
I believe it called a Bucky Ball. After Buckminster Fuller.
A shape in 2D with n sides is called an n-gon. In higher dimensions, a shape with n sides is called an n-sided polyhedron.
A 2D seven sided figure is called a heptagon. A 3D seven faced polygon is called a heptahedron.
A polyhedron with 20 faces is called an icosahedron.
nonahedron
An octahedron, which looks like 2 pyramids glued bottom to bottom.
A 20-sided polyhedron is called an icosahedron. It has 20 equilateral triangle faces, 30 edges, and 12 vertices. It is a regular convex polyhedron with rotational symmetry.
Octohedron
I believe it called a Bucky Ball. After Buckminster Fuller.
Oh, dude, you're looking for a pentagon. It's like a shape with five sides in 2D, but when you add some depth to it, it becomes a pentagonal prism. So, yeah, pentagon is the name you're after.
a polyhedron (if the shape is 3 dimensional) a polygon if it is a planar shape.
A 120-sided polyhedron is a hecatonicosahedron.
A shape in 2D with n sides is called an n-gon. In higher dimensions, a shape with n sides is called an n-sided polyhedron.
A 2D seven sided figure is called a heptagon. A 3D seven faced polygon is called a heptahedron.
In geometry, a hendecagon (also undecagon or endecagon) or 11-gon is an eleven-sided polygon.