Union vs northern

Union is a noun but northern is not a noun.

Word	Noun	Adjective	Verb	Adverb
Union	Yes	Yes	No	No
northern	No	Yes	No	No

Union (noun)	northern (noun)
the United States (especially the northern states during the American Civil War)

Union (adjective)	northern (adjective)
being of or having to do with the northern United States and those loyal to the Union during the American Civil War	situated in regions of the north
	in or characteristic of a region of the United States north of (approximately) the Mason-Dixon line
	coming from the north; used especially of wind
	oriented toward the north