Defense Department vs US Air Force

Defense Department and US Air Force both are nouns.

Word	Noun	Adjective	Verb	Adverb
Defense Department	Yes	No	No	No
US Air Force	Yes	No	No	No

Defense Department (noun)	US Air Force (noun)
the federal department responsible for safeguarding national security of the United States; created in 1947	the airforce of the United States of America; the agency that defends the United States through control and exploitation of air and space