Darth is just an adaptation of the word Dark. The reason George Lucas did this was because Vader meant Father in Dutch so he wanted Darth Vader to mean Darth Father which is what Darth Vader is.
If you don't want to read the other stuff. All of the explanations for their names are in bold letters. General Kenobi! You are a bold one!
Most Sith names that come before the title Darth which is not a name it's a title similar to Christ. Christ is not a last name it's a title given to Jesus. More possible inspiration George took from Religion which I find fascinating.
I will start this post from early Sith then I'll move onto their apprentices and so on to Vader who is the last sith with the title Darth. This list will only be covering Sith with the title Darth so it will not have Kylo Ren or Snoke. So get your Altoids ready cause this might be a long post. For those that don't know Altoids are a good breath mint but enough of the sidetracking let's get into this. Also I will only be covering Sith with a historical presence and who were important to Star Wars.
The list starts below ⬇⬇⬇
Darth Revan was the first Sith to have the title Darth as far as I'm concerned. Revan means "One who is a wonderful horse rider." In Indian. But Revan's name most likely came from the words Revenge or Retaliation. Revan sort of takes revenge in the KOTOR games so this makes sense.
Darth Malak was the apprentice of Darth Revan for a short time. Malak actually means Angel in Arabic which definitely doesn't suit Darth Malak but let's dive deeper. I did research on words that are similar to Malak and a word called Hazar came up. Hazar means Caution, Fear, Prudence I don't know if these terms fit Malak's character cause I never played KOTOR but if it does than I would assume that's where he got his name from.
Darth Nihilus was arguably one of if not the most powerful Sith lord ever. He was always hungry and he would devour planets draining there life forces away and making himself more powerful by doing so. Nihilist is probably the word which inspired Darth Nihilus name it means "one who believes in "the denial of all real existence or the possibility of an objective basis for truth." I don't think this description suits Nihilus very well so let's dive deeper. Not all Sith's names might be real world names as well. Nihilus in the Star Wars universe means Hunger and Nihilus was always known as the Lord of Hunger I think it's safe to say Darth Nihilus name was inspired by the word Nihilus which meant hunger in the Star Wars universe. Darth Nihilus body was so destroyed by the Dark Side that he didn't even have a body it's said his body was just a black gas underneath his pitch black robes if there was even anything there.
Darth Bane was the founder of the Rule of Two where only two Sith may rule at once. He is probably the most important Sith Lord a side from yours truly Darth Sidious. Bane means the cause of high distress or annoyance which Bane clearly does as he is a Sith although I think his name might be after another word so let's dive deeper. Another word for Bane is Curse which would fit Darth Bane's character better in my opinion as he brings a curse for the Sith. The Rule of Two in my opinion is sort of like a curse so it's safe to say Bane got his name from the word curse and destruction which Bane also means destruction or harm. So basically every word that means something bad is what Bane means.
Darth Zannah was the apprentice of Darth Bane. Her name likely came from the words Zannah and Rain and finally Bane. Zannah means alertness. Rain means something happening quickly or obviously water droplets dropping out of the sky but in this case it's something happening quickly. Bane means curse or destruction. So I'm assuming Darth Zannah was a quick and alert Sith who also killed people.
Darth Vectivus stemmed from Darth Bane's Rule of Two. Darth Vectivus name comes from the word Invective which means Abusive. But believe it or not this word doesn't fit Vectivus. Apparently he was the only Sith Lord that never did evil. Maybe his master based the word Invective thinking his apprentice would be evil but he never became evil.
Darth Rampage stemmed from Darth Bane's Rule of Two. He was a humanoid male. He was born 286 BBY his name clearly comes from the word Rampage which means to go on a killing spree. Although I find it difficult to believe he would go on Rampages but he probably did secretly.
Darth Tenebrous is probably one of my favorite Sith I find him very interesting. He was suspected of designing the Scimitar which was the ship used by Darth Maul. He was also the master of Darth Plagueis. He was also a scientist obsessed with preserving his life and he was evil to the core like most Sith Lords were. His name came from the word Tenebrous which meant Dark or gloomy.
Have you ever heard the Tragedy of Darth Plagueis the Wise? It's a Sith legend. Darth Plagueis was a Dark Lord of the Sith, so powerful and so wise he could use the Force to influence the midichlorians to create life…He had such a knowledge of the Dark Side he could even keep the ones he cared about from dying. The Dark Side of the Force is a pathway to many abilities some consider to be Unnatural. He became so powerful, the only thing he was afraid of was losing his power. Unfortunately he taught his apprentice everything he knew, then his apprentice killed him in his sleep, Ironic he could save others from death, but not himself. Darth Plagueis's name comes from the viral Plague which was a horrific disease. It killed hundreds of thousands of people in the real world. And of course it existed in Star Wars as well. Darth Plagueis was the Master to Darth Sidious. He was surprisingly polite and well mannered. For a Sith Lord.
Darth Sidious AKA Sheev Palpatine was the most evil and the most powerful Sith Lord to ever exist. He destroyed the entire Jedi Order. He manipulated and hid under them for 20 years and he deceived the Chosen one Anakin Skywalker into becoming the Sith Lord Darth Vader. His name comes from the word Insidious which means Malevolent and insane. He also killed his Master Darth Plagueis in his sleep and then went on to tell Anakin the Tragedy of Darth Plagueis the Wise. Darth Sidious is clearly Malevolent and insane.
Darth Maul was the apprentice of Darth Sidious. Maul was basically sold to Sidious by his mother Talzin who gave Sidious Maul so he could become a Sith Lord. Eventually Maul was cut in half by Obi-Wan and he eventually hated the Sith. Maul is one of the most interesting and tragic Star Wars characters. His name comes from the word Maul which means big hammer or big axe. Sidious told Plagueis that Maul would just be a assassin and not an actual apprentice which we know was a lie something Sidious is great at. Darth Sidious betrayed Maul
Darth Tyrannus aka Count Dooku was the apprentice of Darth Sidious. Darth Plagueis was actually obsessed with Dooku he found Dooku's power to be astonishing and he was looking to replace Sidious with Dooku causing Sidious to be jealous. Later Dooku and Sidious would form some sort of alliance and Sidious would make Dooku his apprentice and naming him Darth Tyrannus which means Tyrannical something that fits Dooku. Darth Tyrannus was one of the best dueliest's ever in the Galaxy. He was also one of the coolest Sith. Eventually Darth Tyrannus was betrayed by Sidious and beheaded by Anakin Skywalker.
Anakin Skywalker aka Darth Vader is a broken man. He was deceived and corrupted by Darth Sidious. He was groomed to be Sidious's new apprentice ever since he met him in 32 BBY. Sidious knew he would destroy the Jedi by corrupting Anakin who was the Chosen One. Anakin had a higher Midichlorian count than any other Jedi and Sith. He turned fully to the Dark Side when his wife died and when he was scarred and mauled by Obi-Wan in 19 BBY. He was put into a Dark suit of armor and he stayed in that until his death. He carried out Sidious's order to kill all the Jedi in the temple along with the Clones. He was put into a Dark suit of armor and he stayed in that until his death. Throughout 21 years Vader brutally murdered anyone who would dare to make him angry. He routinely hunted down Jedi and brutally murdered them. He was evil until he met his son who redeemed him and he killed Darth Sidious by throwing him down a ventilation shaft. Thus making the prophecy come true. Anakin destroyed the Sith and brought balance to the Force even though he became a Sith. Vader's name means Father in Dutch which is sort of perfect because he is a father but let's dive deeper. Vader according to @CrazyGamer354 means Invader. Which is perfect because he invades the Jedi temple.
Thank you for reading and May the Force be with you, always.