We have starting at the beginning..
Darth Maul - One would assume the name is relevant to his desire to 'maul' jedis and whatnot.
Darth Sidious - Follows through the trilogy, but he is quite the insidious character with his plotting and manipulations behind the scenes
Darth Tyrannus - I'd guess comming from the root Tyrant, though I'm not certain.
Darth Vader - Vader meaning father.
PASS'd if correct enough.