The Collaborative International Dictionary of English v.0.48:

Burr \Burr\ (b[^u]r), n. [See Bur.] (Bot.)
   1. A prickly seed vessel. See Bur, 1.
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   2. The thin edge or ridge left by a tool in cutting or
      shaping metal, as in turning, engraving, pressing, etc.;
      also, the rough neck left on a bullet in casting.
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            The graver, in plowing furrows in the surface of the
            copper, raises corresponding ridges or burrs.
                                                  --Tomlinson.
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   3. A thin flat piece of metal, formed from a sheet by
      punching; a small washer put on the end of a rivet before
      it is swaged down.
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   4. A broad iron ring on a tilting lance just below the gripe,
      to prevent the hand from slipping.
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   5. The lobe or lap of the ear.
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   6. [Probably of imitative origin.] A guttural pronounciation
      of the letter r, produced by trilling the extremity of the
      soft palate against the back part of the tongue; rotacism;
      -- often called the Newcastle burr, Northumberland
      burr, or Tweedside burr.
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   7. The knot at the bottom of an antler. See Bur, n., 8.
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