Yank vs Federal soldier

Yank and Federal soldier both are nouns.

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

As nouns, Federal soldier is a hyponym of Yank; that is, Federal soldier is a word with a more specific, narrower meaning than Yank:

Yank: an American who lives in the North (especially during the American Civil War)
Federal soldier: a member of the Union Army during the American Civil War

Other hyponyms of Yank include Federal, Union soldier.

Yank (noun)	Federal soldier (noun)
an American (especially to non-Americans)	a member of the Union Army during the American Civil War
an American who lives in the North (especially during the American Civil War)