Yankee vs USA

Yankee and USA both are nouns.

Word	Noun	Adjective	Verb	Adverb
Yankee	Yes	Yes	No	No
USA	Yes	No	No	No

Yankee (noun)	USA (noun)
an American (especially to non-Americans)	the army of the United States of America; the agency that organizes and trains soldiers for land warfare
an American who lives in New England	North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776
an American who lives in the North (especially during the American Civil War)

Yankee (adjective)	USA (adjective)
used by Southerners for an inhabitant of a northern state in the United States (especially a Union soldier)