USA vs department of the federal government

USA and department of the federal government both are nouns.

Word	Noun	Adjective	Verb	Adverb
USA	Yes	No	No	No
department of the federal government	Yes	No	No	No

USA (noun)	department of the federal government (noun)
the army of the United States of America; the agency that organizes and trains soldiers for land warfare	a department of the federal government of the United States
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