cow barn vs barn

cow barn and barn both are nouns.

Word	Noun	Adjective	Verb	Adverb
cow barn	Yes	No	No	No
barn	Yes	No	No	No

As nouns, barn is a hypernym of cow barn; that is, barn is a word with a broader meaning than cow barn:

cow barn: a barn for cows
barn: an outlying farm building for storing grain or animal feed and housing farm animals

cow barn (noun)	barn (noun)
a barn for cows	an outlying farm building for storing grain or animal feed and housing farm animals
	(physics) a unit of nuclear cross section; the effective circular area that one particle presents to another as a target for an encounter