The Collaborative International Dictionary of English v.0.48:

Butt \Butt\, But \But\, n. [F. but butt, aim (cf. butte knoll),
   or bout, OF. bot, end, extremity, fr. boter, buter, to push,
   butt, strike, F. bouter; of German origin; cf. OHG. b[=o]zan,
   akin to E. beat. See Beat, v. t.]
   1. A limit; a bound; a goal; the extreme bound; the end.
      [1913 Webster]

            Here is my journey's end, here my butt
            And very sea mark of my utmost sail.  --Shak.
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   Note: As applied to land, the word is nearly synonymous with
         mete, and signifies properly the end line or boundary;
         the abuttal.
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   2. The larger or thicker end of anything; the blunt end, in
      distinction from the sharp end; as, the butt of a rifle.
      Formerly also spelled but. See 2nd but, n. sense 2.
      [1913 Webster +PJC]

   3. A mark to be shot at; a target. --Sir W. Scott.
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            The groom his fellow groom at butts defies,
            And bends his bow, and levels with his eyes.
                                                  --Dryden.
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   4. A person at whom ridicule, jest, or contempt is directed;
      as, the butt of the company.
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            I played a sentence or two at my butt, which I
            thought very smart.                   --Addison.
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   5. A push, thrust, or sudden blow, given by the head of an
      animal; as, the butt of a ram.
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   6. A thrust in fencing.
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            To prove who gave the fairer butt,
            John shows the chalk on Robert's coat. --Prior.
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   7. A piece of land left unplowed at the end of a field.
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            The hay was growing upon headlands and butts in
            cornfields.                           --Burrill.
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   8. (Mech.)
      (a) A joint where the ends of two objects come squarely
          together without scarfing or chamfering; -- also
          called butt joint.
      (b) The end of a connecting rod or other like piece, to
          which the boxing is attached by the strap, cotter, and
          gib.
      (c) The portion of a half-coupling fastened to the end of
          a hose.
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   9. (Shipbuilding) The joint where two planks in a strake
      meet.
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   10. (Carp.) A kind of hinge used in hanging doors, etc.; --
       so named because fastened on the edge of the door, which
       butts against the casing, instead of on its face, like
       the strap hinge; also called butt hinge.
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   11. (Leather Trade) The thickest and stoutest part of tanned
       oxhides, used for soles of boots, harness, trunks.
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   12. The hut or shelter of the person who attends to the
       targets in rifle practice.
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   13. The buttocks; as, get up off your butt and get to work;
       -- used as a euphemism, less objectionable than ass.
       [slang]

   Syn: ass, rear end, derriere, behind, rump, heinie.
        [PJC]

   Butt chain (Saddlery), a short chain attached to the end of
      a tug.

   Butt end. The thicker end of anything. See But end, under
      2d But.
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            Amen; and make me die a good old man!
            That's the butt end of a mother's blessing. --Shak.
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   A butt's length, the ordinary distance from the place of
      shooting to the butt, or mark.

   Butts and bounds (Conveyancing), abuttals and boundaries.
      In lands of the ordinary rectangular shape, butts are the
      lines at the ends (F. bouts), and bounds are those on the
      sides, or sidings, as they were formerly termed.
      --Burrill.

   Bead and butt. See under Bead.

   Butt and butt, joining end to end without overlapping, as
      planks.

   Butt weld (Mech.), a butt joint, made by welding together
      the flat ends, or edges, of a piece of iron or steel, or
      of separate pieces, without having them overlap. See
      Weld.

   Full butt, headfirst with full force. [Colloq.] "The
      corporal . . . ran full butt at the lieutenant."
      --Marryat.
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The Collaborative International Dictionary of English v.0.48:

Butt joint \Butt" joint`\
   A joint in which the edges or ends of the pieces united come
   squarely together instead of overlapping. See 1st Butt, 8.
   [1913 Webster]

WordNet (r) 3.0 (2006):

butt joint
    n 1: a joint made by fastening ends together without overlapping
         [syn: butt joint, butt]