duct vs air passage

duct and air passage both are nouns.

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

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

Other hyponyms of duct include air-intake, air duct, airway.

duct (noun)	air passage (noun)
an enclosed conduit for a fluid	a duct that provides ventilation (as in mines)
a bodily passage or tube lined with epithelial cells and conveying a secretion or other substance
a continuous tube formed by a row of elongated cells lacking intervening end walls