city vs Cancun

city and Cancun both are nouns.

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

city (noun)	Cancun (noun)
people living in a large densely populated municipality	a popular island resort off the northeastern tip of the Yucatan peninsula
a large and densely populated urban area; may include several independent administrative districts
an incorporated administrative district established by state charter