city vs city district

city and city district both are nouns.

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

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