air passage vs upcast

air passage and upcast both are nouns.

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

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

air passage: a duct that provides ventilation (as in mines)
upcast: air passage consisting of a ventilation shaft through which air leaves a mine

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

air passage (noun)	upcast (noun)
a duct that provides ventilation (as in mines)	air passage consisting of a ventilation shaft through which air leaves a mine