secondary vs junior-grade

secondary is a noun but junior-grade is not a noun.

Word	Noun	Adjective	Verb	Adverb
secondary	Yes	Yes	No	No
junior-grade	No	Yes	No	No

As adjectives, secondary and junior-grade are synonyms defined as:

Other synonyms of secondary include lower-ranking, lowly, petty, subaltern.

secondary (noun)	junior-grade (noun)
coil such that current is induced in it by passing a current through the primary coil
the defensive football players who line up behind the linemen

secondary (adjective)	junior-grade (adjective)
being of second rank or importance or value; not direct or immediate	inferior in rank or status
depending on or incidental to what is original or primary
inferior in rank or status
not of major importance
belonging to a lower class or rank