The Collaborative International Dictionary of English v.0.48:

Arris \Ar"ris\, n. [OF. areste, F. ar[^e]te, fr. L. arista the
   top or beard of an ear of grain, the bone of a fish.] (Arch.)
   The sharp edge or salient angle formed by two surfaces
   meeting each other, whether plane or curved; -- applied
   particularly to the edges in moldings, and to the raised
   edges which separate the flutings in a Doric column. --P.
   Cyc.
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   Arris fillet, a triangular piece of wood used to raise the
      slates of a roof against a chimney or wall, to throw off
      the rain. --Gwilt.

   Arris gutter, a gutter of a V form fixed to the eaves of a
      building. --Gwilt.
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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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