Jen'ari was the word in the Sith for "Dark Lord." It was originally used to delineate the Exiles who survived the Hundred-Year Darkness. Thus, it gave rise to the title of the Dark Lord of the Sith.
Sources[]
Evil Never Dies: The Sith Dynasties on Hyperspace (article) (content removed from StarWars.com; backup link) (First mentioned)- Knights of the Old Republic Campaign Guide
- The Complete Star Wars Encyclopedia
- Book of Sith: Secrets from the Dark Side