billion vs U.S.A.

billion and U.S.A. both are nouns.

Word	Noun	Adjective	Verb	Adverb
billion	Yes	Yes	No	No
U.S.A.	Yes	No	No	No

billion (noun)	U.S.A. (noun)
the number that is represented as a one followed by 9 zeros	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
the number that is represented as a one followed by 12 zeros; in the United Kingdom the usage followed in the United States is frequently seen
a very large indefinite number (usually hyperbole)

billion (adjective)	U.S.A. (adjective)
denoting a quantity consisting of one thousand million items or units in the United States
denoting a quantity consisting of one million million items or units in Great Britain