Sith (pronounced shee) means “spirit” in Gaelic. In particular, it’s a reference to the Leannain Sith (lanan-shi) or familiar spirits, which are described as somewhat similar to succubi. (Magonia, 118)
In the Star Wars mythology as written by George Lucas , the Sith (pronounced sith) are a red and black-skinned race with devilish horns who serve as warriors of evil. The Sith are in the same ethnic tradition of the Sand People and the Jawa: the dark, dirty races at the edges of Empire, who are — just coincidentally — the bad guys.