It helps to understand the evolution of the words. Look at the pics on
this page. The first is a 3 piece which consists of a battery, a cartridge and an atomizer. At that time the atomizer was just the piece that heated the liquid turning it to vapor.
Somewhere along the line the atomizer and cartridge were combined to one piece and that was a cartomizer.
Some people wanted to see the liquid levels so some cartomizers were made clear. This was the first clearomizer. Eventually those started to get bigger and evolved to have replaceable parts. Just look up the difference between CE2, CE3 and CE4.
ETA - I stopped at CE4 because after that every company started doing their own numbering system to the point a CE4+, CE5 and CE6 could all be the exact same thing or totally different.
So now that you know the evolution - Some people use all three terms interchangeably but they really aren't interchangeable.