\Flue\, n. [Cf. OF. flue a flowing, fr. fluer to flow, fr.
L. fluere (cf. {Fluent}); a perh. a corruption of E. flute.]
An inclosed passage way for establishing and directing a
current of air, gases, etc.; an air passage; esp.:
(a) A compartment or division of a chimney for conveying
    flame and smoke to the outer air.
(b) A passage way for conducting a current of fresh, foul, or
    heated air from one place to another.
(c) (Steam Boiler) A pipe or passage for conveying flame and
    hot gases through surrounding water in a boiler; --
    distinguished from a tube which holds water and is
    surrounded by fire. Small flues are called fire tubes or
    simply tubes.
{Flue boiler}. See under {Boiler}.
{Flue bridge}, the separating low wall between the flues and
   the laboratory of a reverberatory furnace.
{Flue plate} (Steam Boiler), a plate to which the ends of the
   flues are fastened; -- called also {flue sheet}, {tube
   sheet}, and {tube plate}.
{Flue surface} (Steam Boiler), the aggregate surface of flues
   exposed to flame or the hot gases.

\Flue\, n. [Cf. F. flou light, tender, G. flau weak, W.
llwch dust. [root]84.]
Light down, such as rises from cotton, fur, etc.; very fine
lint or hair. --Dickens.

\Flue\, n.
In an organ flue pipe, the opening between the lower lip and
the languet.