Union Army vs regular army

Union Army and regular army both are nouns.

Word	Noun	Adjective	Verb	Adverb
Union Army	Yes	No	No	No
regular army	Yes	No	No	No

As nouns, regular army is a hypernym of Union Army; that is, regular army is a word with a broader meaning than Union Army:

Union Army: the northern army during the American Civil War
regular army: a permanent organization of the military land forces of a nation or state

Other hypernyms of Union Army include army, ground forces, blue.

Union Army (noun)	regular army (noun)
the northern army during the American Civil War	a permanent organization of the military land forces of a nation or state