lowly vs subaltern

lowly is not a noun while subaltern is a noun.

Word	Noun	Adjective	Verb	Adverb
lowly	No	Yes	No	No
subaltern	Yes	Yes	No	No

As adjectives, lowly and subaltern are synonyms defined as:

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

lowly (noun)	subaltern (noun)
	a British commissioned army officer below the rank of captain

lowly (adjective)	subaltern (adjective)
low or inferior in station or quality	inferior in rank or status
inferior in rank or status
of low birth or station (`base' is archaic in this sense)
used of unskilled work (especially domestic work)