define flue
flue (plural flues) A pipe or duct that carries gaseous combustion products away from the point of combustion (such as a furnace). An enclosed passageway in which to direct air or other gaseous current along. (obsolete, countable and uncountable) A woolly or downy substance; down, nap; a piece of this. In an organ flue pipe, the opening between the lower lip and the languet.