U.S. vs Yankee

U.S. and Yankee both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
Yankee	Yes	Yes	No	No

U.S. (noun)	Yankee (noun)
the executive and legislative and judicial branches of the federal government of the United States	an American (especially to non-Americans)
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 New England
	an American who lives in the North (especially during the American Civil War)

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