Well done!
Hmm, no, but I think Darth (Dark Lord of the Sith) had its meaning pretty early storywise, but no not mentioned in the films.
Cheers
Edit. I found this:
"The first use of the word "Sith" is in the Star Wars novelization for Star Wars Episode IV: A New Hope, as a title for Darth Vader, the "Dark Lord of the Sith." The word is not used in any of the original Star Wars films. The Sith are introduced on-screen with the prequel film Star Wars Episode I: The Phantom Menace), where the order is represented by Darth Sidious and Darth Maul."
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