The story
Blend of Revenge of the Sith + sixth. From the name of the Star Wars movie Episode III – Revenge of the Sith, and a day of the month of similar sound to "Sith".
Etymology from Wiktionary, CC BY-SA 4.0.
Revenge of the Sixth
Today it means: The Sixth of May (May 6). The third Star Wars Day, the second day after Revenge of the Fifth (May 5). Sometimes used to celebrate the Dark Side, when May 4 is used to celebrate the Jedi. Full definition →