open-air market vs marketplace

open-air market and marketplace both are nouns.

Word	Noun	Adjective	Verb	Adverb
open-air market	Yes	No	No	No
marketplace	Yes	No	No	No

As nouns, marketplace is a hypernym of open-air market; that is, marketplace is a word with a broader meaning than open-air market:

open-air market: a public marketplace where food and merchandise is sold
marketplace: an area in a town where a public mercantile establishment is set up

Other hypernyms of open-air market include market, market place, mart.

open-air market (noun)	marketplace (noun)
a public marketplace where food and merchandise is sold	the world of commercial activity where goods and services are bought and sold
	an area in a town where a public mercantile establishment is set up