secondary school vs middle school

secondary school and middle school both are nouns.

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

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

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

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

secondary school (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