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]

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]

WordNet (r) 3.0 (2006):

flue
    n 1: flat bladelike projection on the arm of an anchor [syn:
         fluke, flue]
    2: organ pipe whose tone is produced by air passing across the
       sharp edge of a fissure or lip [syn: flue pipe, flue,
       labial pipe]
    3: a conduit to carry off smoke

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "flue":
   air, blubber, breeze, bubble, butter, chaff, chimney,
   chimney corner, chip, clay, cobweb, cork, cushion, dough, down,
   dust, eiderdown, ether, fairy, feather, feather bed, feathers,
   fender, fire screen, fireboard, fireguard, fireplace, fireside,
   fleece, floss, flue pipe, fluff, foam, froth, fumarole, funnel,
   fur, fuzz, gossamer, hearth, hearthstone, hob, hub, ingle,
   inglenook, ingleside, kapok, lint, mote, pile, pillow, plush,
   pudding, puff, putty, rubber, satin, silk, smokehole, smokeshaft,
   smokestack, sponge, spume, stack, stovepipe, straw, swansdown,
   thistledown, velvet, wax, wool, zephyr