In my head I'd been pronouncing it "RAY-dee-us," like "radius" (and I pronounced Rhaiod "RAY-odd"), but recently it occurred to me that's probably wrong.

I figure "rah-DAY-iss" or "RAH-day-iss" (and "RAI-odd" for "Rhaiod") would be the most phonetically accurate pronunciation based on spelling alone, but the only way to know for sure is straight from the horse's mouth.