air passage vs breather

air passage and breather both are nouns.

Word	Noun	Adjective	Verb	Adverb
air passage	Yes	No	No	No
breather	Yes	No	No	No

As nouns, breather is a hyponym of air passage; that is, breather is a word with a more specific, narrower meaning than air passage:

air passage: a duct that provides ventilation (as in mines)
breather: air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time

Other hyponyms of air passage include register, schnorchel, schnorkel, snorkel, snorkel breather, upcast, ventilation shaft.

air passage (noun)	breather (noun)
a duct that provides ventilation (as in mines)	air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time
	a short respite