city-state vs city state

city-state and city state both are nouns.

Word	Noun	Adjective	Verb	Adverb
city-state	Yes	No	No	No
city state	Yes	No	No	No

As nouns, city-state and city state are synonyms defined as:

city-state (noun)	city state (noun)
a state consisting of a sovereign city	a state consisting of a sovereign city