grammar vs contrastive

grammar is a noun but contrastive is not a noun.

Word	Noun	Adjective	Verb	Adverb
grammar	Yes	No	No	No
contrastive	No	Yes	No	No

grammar (noun)	contrastive (noun)
the branch of linguistics that deals with syntax and morphology (and sometimes also deals with semantics)

grammar (adjective)	contrastive (adjective)
	of words so related that one contrasts with the other
	strikingly different; tending to contrast
	syntactically establishing a relation of contrast between sentences or elements of a sentence