Well, I would have called our middle school “γυμνάσιο”/“gymnasium” like we do here, but people like @Sanonius that are actually being taught ancient Greek might take things literally and think that we go to school naked 
I still do not know why we call it like that … kids have clothes in Greece, damn it 
Oh, there are a lot of words that are “lost” like that or are very very obscure … a very old school teacher here is a linguist of sorts and he is writting a book on the matter called “Lexignosia”/Λεξιγνωσία or “knowledge of words” if one was to translate that neologism in English. I am helping him typeset the book since he is so old that he has no clue about computers and in that process I have learned about a lot of ancient Greek words that serve as “roots” for modern words.
Indeed the modern language stands on some very solid ground set by the ancients, which is why it seems to change in a slower manner.
For example, there is an ancient root/word for the word “stone” named “Λας” … noone uses that today, but a quarry in modern Greek is still called a Λα-τομίο, which literally means “a place where you cut stones” (Λας = rock/stone + τομή = cut).
Or the word “άρουρα” which means earth/the ground … it is used in Homer when, if I remember correctly, Achilles calls himself “άχθος αρούρης” = a weight upon the earth, which is a poetic way to say that he was totally useless.
Well, noone uses the word άρουρα to describe the ground anymore, but the word for the ground rat is still “αρουραίος” which literally means something “of the ground”/“that lives in/on the ground”
It is all so very interesting. I wish school included fun things like that …
If you’d like I could send it to you in pdf once it is ready … we are in the last proof-reading process at the moment and it is 100 pages of quite good linguistic analysis with some occassional hypothetical linguistic gymnastics, but they still make a lot of sense and are very educative.