The Collaborative International Dictionary of English v.0.48:

Muzzle \Muz"zle\, n. [OE. mosel, OF. musel, F. museau muzzle or
   snout, LL. musellus, fr. musus, morsus. See Muse, v. i.,
   and cf. Morsel.]
   1. The projecting mouth and nose of a quadruped, as of a
      horse; a snout.
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   2. The mouth of a thing; the end for entrance or discharge;
      as, the muzzle of a gun.
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   3. A fastening or covering (as a band or cage) for the mouth
      of an animal, to prevent eating or vicious biting.
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            With golden muzzles all their mouths were bound
                                                  --Dryden.
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   Muzzle sight. (Gun.) See Dispart, n., 2.
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The Collaborative International Dictionary of English v.0.48:

Dispart \Dis*part"\, n.
   1. (Gun.) The difference between the thickness of the metal
      at the mouth and at the breech of a piece of ordnance.
      [1913 Webster]

            On account of the dispart, the line of aim or line
            of metal, which is in a plane passing through the
            axis of the gun, always makes a small angle with the
            axis.                                 --Eng. Cys.
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   2. (Gun.) A piece of metal placed on the muzzle, or near the
      trunnions, on the top of a piece of ordnance, to make the
      line of sight parallel to the axis of the bore; -- called
      also dispart sight, and muzzle sight.
      [1913 Webster]