combat zone vs city district

combat zone and city district both are nouns.

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

As nouns, city district is a hypernym of combat zone; that is, city district is a word with a broader meaning than combat zone:

combat zone (noun)	city district (noun)
a military area where combat forces operate	a district of a town or city
a city district known for its vice and high crime rate