contrastive vs grammar

contrastive is not a noun while grammar is a noun.

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

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

contrastive (adjective)	grammar (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