air duct vs breather

air duct and breather both are nouns.

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

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

air duct: 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 duct include register, schnorchel, schnorkel, snorkel, snorkel breather, upcast, ventilation shaft.

air duct (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