urban vs city

urban is not a noun while city is a noun.

Word	Noun	Adjective	Verb	Adverb
urban	No	Yes	No	No
city	Yes	No	No	No

urban (noun)	city (noun)
	people living in a large densely populated municipality
	a large and densely populated urban area; may include several independent administrative districts
	an incorporated administrative district established by state charter

urban (adjective)	city (adjective)
located in or characteristic of a city or city life
relating to or concerned with a city or densely populated area