national capital vs Forbidden City

national capital and Forbidden City both are nouns.

Word	Noun	Adjective	Verb	Adverb
national capital	Yes	No	No	No
Forbidden City	Yes	No	No	No

national capital (noun)	Forbidden City (noun)
the capital city of a nation	a walled section of Beijing that encloses the palace that was formerly the residence of the emperor of China
	the sacred city of Lamaism; known as the Forbidden City for its former inaccessibility and hostility to strangers