If in doubt, stick an apostrophe in th'ere.
This is still better than George Lucas's approach of using common words to become character names because they fit the character attribute. Take Darth Sideous - I guess he was called that because he is evil and INSIDIOUS.
Well, yeah. That was kind of the whole point.

They're not family names, they're made up names Sith Lords give themselves or their apprentices. The Emperor wasn't Joe Sidious IV of the Naboo Sidious'.
In a galaxy where they speak the Star Warsian equivalent of English (with all the languages English has borrowed from included) and words like insidious, plague, invader, tyranny, bane, and maul have meaning, why wouldn't they give themselves a badass name to both conceal their true identities and inspire fear in their enemies?
"Uh oh, here comes Dooku" sounds like you're about to have an accident in your pants and doesn't exactly carry the same weight as "Uh oh, here comes Tyrannus." Yeah, it's a bit on the simplistic mustache-twirling curse your sudden but inevitable betrayal side, but since Star Wars is based on old movie serials where that kind of villain would fit right in, it makes sense.