Yankee vs United States

Yankee and United States both are nouns.

Word	Noun	Adjective	Verb	Adverb
Yankee	Yes	Yes	No	No
United States	Yes	No	No	No

Yankee (noun)	United States (noun)
an American (especially to non-Americans)	the executive and legislative and judicial branches of the federal government of the United States
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)	United States (adjective)
used by Southerners for an inhabitant of a northern state in the United States (especially a Union soldier)