city vs Motor City

city and Motor City both are nouns.

Word	Noun	Adjective	Verb	Adverb
city	Yes	No	No	No
Motor City	Yes	No	No	No

city (noun)	Motor City (noun)
people living in a large densely populated municipality	the largest city in Michigan and a major Great Lakes port; center of the United States automobile industry; located in southeastern Michigan on the Detroit river across from Windsor
a large and densely populated urban area; may include several independent administrative districts
an incorporated administrative district established by state charter