Hello, some additions from my notes that you might find interesting! (Sorry to be a bother haha.)
Ashe - could be derived from the ash tree: "The tree's common English name, "ash", traces back to the Old English æsc which relates to the Proto-Indo-European for the tree, while the generic name originated in Latin from a Proto-Indo-European word for birch. Both words are also used to mean "spear" in their respective languages as the wood is good for shafts." (Faerghus warriors are well known for their prowess with spears!)
I also think it might be worth noting just how many of these names are connected to religion, especially the Roman Catholic Church. (I find this especially fascinating because I did some reading on heraldry, and eagles are a symbol of the Roman empire; they are featured on the flag for the "King of the Romans"/"King of Germany." And only one of our lords has a German name... and is also the leader of the Black Eagles. Coincidence?)
Byleth, of course, is the name of the king of Hell.
Petra is the feminine form of Peter, who was an apostle as well as a saint.
Dorothea, Caspar, Bernadetta, and Hubert all share their names with saints. (Interestingly enough, all of these characters also happen to be in the Black Eagles/from the Adrestian Empire. That means 5/8 of Black Eagle characters have names connected to saints!)
Dmitri, derived from the Greek name Demetrius/Demetrios, shares his name with a Saint Demetrius who was run through with spears in 306 AD. (D:)
Felix, Hilda, and Catherine also share their names with saints.
Mercedes is a name referencing the Virgin Mary.
Raphael was an archangel responsible for healing in Abrahamic religions (or in Christianity, he's associated with an unnamed angel in the Gospel of John).
Marianne is the French version of the Greek Mariamne, which is a variant of Mary, ultimately from the Hebrew Miriam, sister of Moses and a prophetess who first appears in the Book of Exodus.
Manuela is the feminine form of the Spanish and Portuguese given name "Manuel", which is in turn derived from the Hebrew name "Emanuel," meaning "God is with us."
Ronato is derived from Renato, which in turn is derived from the Latin name Renatus which means "born again." This is meant in the spiritual sense, as in "to be born again with baptism."
I also find it interesting that three important figures in the story so far (Rhea, Sothis, and Nemesis) are named after goddesses from Greek and Egyptian mythos (or in the case of Rhea, possibly also Roman mythos) while Seiros is a name with Greek origins- cultures that were ultimately conquered by the Romans.
Sylvain (Roman) and Lysithea (Greek) are the only students named after mythological figures/deities (depending on the source) who, as far as we've seen, aren't connected to Rhea, Sothis, or Nemesis, the only ones in the story who also have mythological names.
Also also! There are two names relating to lions (Linhardt and Leonie) that aren't in the Blue Lions house... they may somehow have a connection with the Holy Kingdom of Faerghus? (Since Jeralt's name has a reference to a spear and Leonie was one of his top students, maybe she was originally from Faerghus?)
This is becoming more speculation than etymology but still! I think it's all really fascinating, haha.
