air duct vs snorkel

air duct and snorkel both are nouns.

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

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

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

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