junior-grade vs subaltern

junior-grade is not a noun while subaltern is a noun.

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

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

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

junior-grade (noun)	subaltern (noun)
	a British commissioned army officer below the rank of captain

junior-grade (adjective)	subaltern (adjective)
inferior in rank or status	inferior in rank or status