air passage vs snorkel

air passage and snorkel both are nouns.

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

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

air passage: a duct that provides ventilation (as in mines)
snorkel: 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, breather, schnorchel, schnorkel, snorkel breather, upcast, ventilation shaft.

air passage (noun)	snorkel (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
	breathing device consisting of a bent tube fitting into a swimmer's mouth and extending above the surface; allows swimmer to breathe while face down in the water

air passage (verb)	snorkel (verb)
	dive with a snorkel