The Collaborative International Dictionary of English v.0.48:

Fillet \Fil"let\, n. [OE. filet, felet, fr. OF. filet thread,
   fillet of meat, dim. of fil a thread, fr. L. filum. See
   Fille a row.]
   1. A little band, especially one intended to encircle the
      hair of the head.
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            A belt her waist, a fillet binds her hair. --Pope.
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   2. (Cooking) A piece of lean meat without bone; sometimes, a
      long strip rolled together and tied.
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   Note: A fillet of beef is the under side of the sirlom; also
         called tenderloin. A fillet of veal or mutton is the
         fleshy part of the thigh. A fillet of fish is a slice
         of flat fish without bone. "Fillet of a fenny snake."
         --Shak.
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   3. A thin strip or ribbon; esp.:
      (a) A strip of metal from which coins are punched.
      (b) A strip of card clothing.
      (c) A thin projecting band or strip.
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   4. (Mach.) A concave filling in of a re["e]ntrant angle where
      two surfaces meet, forming a rounded corner.
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   5. (Arch.) A narrow flat member; especially, a flat molding
      separating other moldings; a reglet; also, the space
      between two flutings in a shaft. See Illust. of Base,
      and Column.
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   6. (Her.) An ordinary equaling in breadth one fourth of the
      chief, to the lowest portion of which it corresponds in
      position.
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   7. (Mech.) The thread of a screw.
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   8. A border of broad or narrow lines of color or gilt.
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   9. The raised molding about the muzzle of a gun.
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   10. Any scantling smaller than a batten.
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   11. (Anat.) A fascia; a band of fibers; applied esp. to
       certain bands of white matter in the brain.
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   12. (Man.) The loins of a horse, beginning at the place where
       the hinder part of the saddle rests.
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   Arris fillet. See under Arris.
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The Collaborative International Dictionary of English v.0.48:

Fillet \Fil"let\, v. t. [imp. & p. p. Filleted; p. pr. & vb.
   n. Filleting.]
   To bind, furnish, or adorn with a fillet.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fillet
    n 1: a boneless steak cut from the tenderloin of beef [syn:
         fillet, filet]
    2: a longitudinal slice or boned side of a fish [syn: fillet,
       filet, fish fillet, fish filet]
    3: a bundle of sensory nerve fibers going to the thalamus [syn:
       lemniscus, fillet]
    4: a narrow headband or strip of ribbon worn as a headband [syn:
       taenia, tenia, fillet]
    5: fastener consisting of a narrow strip of welded metal used to
       join steel members [syn: fillet, stopping]
    v 1: decorate with a lace of geometric designs [syn: fillet,
         filet]
    2: cut into filets; "filet the fish" [syn: fillet, filet]