concrete jungle vs metropolis

concrete jungle and metropolis both are nouns.

Word	Noun	Adjective	Verb	Adverb
concrete jungle	Yes	No	No	No
metropolis	Yes	No	No	No

concrete jungle (noun)	metropolis (noun)
an area in a city with large modern buildings that is perceived as dangerous and unpleasant	people living in a large densely populated municipality
	a large and densely populated urban area; may include several independent administrative districts