city vs Houston

city and Houston both are nouns.

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

city (noun)	Houston (noun)
people living in a large densely populated municipality	the largest city in Texas; located in southeastern Texas near the Gulf of Mexico; site of the National Aeronautics and Space Administration
a large and densely populated urban area; may include several independent administrative districts	United States politician and military leader who fought to gain independence for Texas from Mexico and to make it a part of the United States (1793-1863)
an incorporated administrative district established by state charter