flue

noun4

1. •
   A pipe or duct that carries gaseous combustion products away from the point of combustion (such as a furnace).
2. •
   An enclosed passageway in which to direct a current of air or other gases along.
3. •
   In an organ flue pipe, the opening between the lower lip and the languet.
4. •
   (no longer used) A woolly or downy substance; down, nap; a piece of this.