U.S.A. vs old man

U.S.A. and old man both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.A.	Yes	No	No	No
old man	Yes	No	No	No

U.S.A. (noun)	old man (noun)
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 informal term for your father
	a man who is very old
	a familiar term of address for a man
	(slang) boss
	aromatic herb of temperate Eurasia and North Africa having a bitter taste used in making the liqueur absinthe