Gymnasium vs middle school

Gymnasium and middle school both are nouns.

Word	Noun	Adjective	Verb	Adverb
Gymnasium	Yes	No	No	No
middle school	Yes	No	No	No

As nouns, Gymnasium and middle school are synonyms defined as:

Gymnasium and middle school: a school for students intermediate between elementary school and college; usually grades 9 to 12

Other synonyms of Gymnasium include lycee, lyceum, secondary school.

Gymnasium (noun)	middle school (noun)
a school for students intermediate between elementary school and college; usually grades 9 to 12	a school for students intermediate between elementary school and college; usually grades 9 to 12