metropolis vs central city

metropolis and central city both are nouns.

Word	Noun	Adjective	Verb	Adverb
metropolis	Yes	No	No	No
central city	Yes	No	No	No

metropolis (noun)	central city (noun)
people living in a large densely populated municipality	the central part of a city
a large and densely populated urban area; may include several independent administrative districts