borderline vs marginal

borderline is a noun but marginal is not a noun.

Word	Noun	Adjective	Verb	Adverb
borderline	Yes	Yes	No	No
marginal	No	Yes	No	No

As adjectives, borderline and marginal are synonyms defined as:

borderline (noun)	marginal (noun)
a line that indicates a boundary

borderline (adjective)	marginal (adjective)
of questionable or minimal quality	of questionable or minimal quality
	just barely adequate or within a lower limit
	at or constituting a border or edge
	producing at a rate that barely covers production costs