It's pronounced like 'heed-ron'

Prior to google, my second grade teacher Mrs Graber was the best teacher I ever had.

But could she, within a moment, a blink of an eye, a micromillivanilli second, shorter than it takes me to write one word of this, have answered correctly when my five-year-old niece asked, "What is a three dimensional octagon called?"

A 3-dimensional shape with eight sides would be 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.

~wiki answers

...