Most writers coming up with alien names aren't deriving them from Latin or Greek. Some are -- there are obvious cases like "Romulan" -- but usually they're just making up alien-sounding words, maybe going for a certain subjective flavor, rather than worrying about formal etymology.
We actually know the origin of the name "Cardassian" from its creator:
Jeri Taylor – an executive producer for TNG and the writer of "The Wounded", the first episode to feature the Cardassians – invented the group name for the species. "I came up with 'Circassians' which I thought had a vaguely alien sound, though something in the back of my mind thought it came too easily," Taylor explained. "And someone (probably Joe Menosky) pointed out that the Circassians were a real people on Earth, in antiquity. So I just played around with the sounds and 'Cardassian' kind of fell into place."
This is why research is better than guesswork.