U.S. vs freshman

U.S. and freshman both are nouns.

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

U.S. (noun)	freshman (noun)
the executive and legislative and judicial branches of the federal government of the United States	a first-year undergraduate
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	any new participant in some activity

U.S. (adjective)	freshman (adjective)
	used of a person in the first year of an experience (especially in United States high school or college)