From The Collaborative International Dictionary of English v.0.48:
Flue \Flue\ (fl[=u]), 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.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
Flue \Flue\ (fl[=u]), n. [Cf. OF. flue a flowing, fr. fluer to
flow, fr. L. fluere (cf. Fluent); a perh. a corruption of
E. flute.]
1. 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.
[1913 Webster]
2. In an organ flue pipe, the opening between the lower lip
and the languet.
[Webster 1913 Suppl.]
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.
[1913 Webster]