decorative vs ornamental

decorative is not a noun while ornamental is a noun.

Word	Noun	Adjective	Verb	Adverb
decorative	No	Yes	No	No
ornamental	Yes	Yes	No	No

As adjectives, decorative and ornamental are synonyms defined as:

decorative and ornamental: serving an esthetic rather than a useful purpose

Other synonyms of decorative include cosmetic.

decorative (noun)	ornamental (noun)
	any plant grown for its beauty or ornamental value

decorative (adjective)	ornamental (adjective)
serving an esthetic rather than a useful purpose	serving an esthetic rather than a useful purpose