schnorkel vs air passage

schnorkel and air passage both are nouns.

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

As nouns, air passage is a hypernym of schnorkel; that is, air passage is a word with a broader meaning than schnorkel:

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

Other hypernyms of schnorkel include air duct, airway.

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