USA vs Mel Gibson

USA and Mel Gibson both are nouns.

Word	Noun	Adjective	Verb	Adverb
USA	Yes	No	No	No
Mel Gibson	Yes	No	No	No

USA (noun)	Mel Gibson (noun)
the army of the United States of America; the agency that organizes and trains soldiers for land warfare	Australian actor (born in the United States in 1956)
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