Also, is there such thing as Archduke? I've seen that tilte appear quite a bit but can never seem to figure out where its place is.
So there's actually quite a lot of different titles of nobility (here's a
wikipedia article with a list on the right), Archduke was a title used used by the von habsburgs of austria to diferentiate them from other dukes, the word appears once before because there was a guy who was both a duke and an archbishop, but the title as we understand it now was just the austrians bullshitting their way into saying they were more special than a regular duke with a
forged document.
It's important to understand that these titles don't necessarily have a rigid definition and their meaning can change depending on time and place
For example, in the roman republic princeps was originally the leader of the senate and was not a hereditary/monarchical title, this was the title used by Augustus (the first emperor) after becomeing de facto monarch, as the romans despised the idea of kings.