A six faced 3d shape is called a cube.
Enneahedral
A hendecahedron.
A twelve sided shape is called a "dodecahedron" :D
A pyramid.
Decahedreon
It is a nonahedron.
Dodecahedron.
It is called a trihedron. It does not exist.
A cube or a cuboid
An eight-faced 3D shape is called an octahedron. Any 3D shape (polyhedron) ends in -hedron, just like any 2D shape (polygon) ends in -gon, and octa- means 8.
Any six-sided shape is a hexagon.