barn vs area unit

barn and area unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
barn	Yes	No	No	No
area unit	Yes	No	No	No

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

barn: (physics) a unit of nuclear cross section; the effective circular area that one particle presents to another as a target for an encounter
area unit: a system of units used to measure areas

Other hypernyms of barn include square measure.

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