Union soldier vs Federal soldier

Union soldier and Federal soldier both are nouns.

Word	Noun	Adjective	Verb	Adverb
Union soldier	Yes	No	No	No
Federal soldier	Yes	No	No	No

As nouns, Union soldier and Federal soldier are synonyms defined as:

Union soldier and Federal soldier: a member of the Union Army during the American Civil War

Other synonyms of Union soldier include Federal.

Union soldier (noun)	Federal soldier (noun)
a member of the Union Army during the American Civil War	a member of the Union Army during the American Civil War