cube square prism
Octagonal prism
2
An octagonal prism
Octagonal prism
octagonal prism
hasarafazoid
a cone
A tetrahedron.
Because it's a 3 dimensional shape that has surface area and volume.
There is no such shape.
A 3-dimensional shape with eight sides is an octahedron. If you would refer to a 3-dimensional octagon, just call it that, people will understand what you mean. Or maybe you mean an octagonal prism. That's an octagon, except it is extended into the third dimension by stretching it, so it has an octagonal base but the other sides are triangles all connecting at one point above the octagon.
Heptagonal pyramids, if you consider the base a side. Octagonal pyramids, if you don't.