eastern United States vs eastern

eastern United States is a noun but eastern is not a noun.

Word	Noun	Adjective	Verb	Adverb
eastern United States	Yes	No	No	No
eastern	No	Yes	No	No

eastern United States (noun)	eastern (noun)
the region of the United States lying to the north of the Ohio River and to the east of the Mississippi River

eastern United States (adjective)	eastern (adjective)
	relating to or characteristic of regions of eastern parts of the world
	of or characteristic of eastern regions of the United States
	lying toward or situated in the east
	from the east; used especially of winds
	lying in or toward the east