#duct.conduit  an enclosed conduit for a fluid
  supertype:  #conduit__channel  a passage for water (or other fluids)
  subtype:  #air-intake__airintake  a duct that admits air to be mixed with fuel
  subtype:  #air_passage__airpassage__air_duct__airduct__airway  a duct that provides ventilation as in mines
     subtype:  #register.air_passage  an air passage (usually in the floor or a wall of a room) for admitting or excluding heated air from the room
     subtype:  #snorkel_breather__snorkelbreather__snorkel__schnorchel__breather  air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time
     subtype:  #upcast  air passage consisting of a ventilation shaft through which air leaves a mine
     subtype:  #ventilation_shaft__ventilationshaft  a shaft in a building; serves as an air passage for ventilation

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