Wiktionary
air duct
n. A duct, through which air is forced or extracted, that forms part of a building's air conditioning and ventilation system.
WordNet
air duct
n. a duct that provides ventilation (as in mines) [syn: air passage, airway]
Usage examples of "air duct".
I winked at Susan, picked up the duck, and entered the air duct, moving as quietly as I could.
Ba'tra would normally have sent a team through an air duct, or tried to lure the enemy out by feigning withdrawal.
In the utter darkness of the air duct, he had to keep his mental map of the station constantly in mind.
Then they attached a flexible plastic air duct to the hole, taping all the cracks with sticky duct tape.
The corporal slung her upwards as if she were weightless, and she pulled herself into the air duct with a muffled grunt.