The Collaborative International Dictionary of English v.0.48:

Carrier \Car"ri*er\, n. [From Carry.]
   1. One who, or that which, carries or conveys; a messenger.
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            The air which is but . . . a carrier of the sounds.
                                                  --Bacon.
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   2. One who is employed, or makes it his business, to carry
      goods for others for hire; a porter; a teamster.
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            The roads are crowded with carriers, laden with rich
            manufactures.                         --Swift.
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   3. (Mach.) That which drives or carries; as:
      (a) A piece which communicates to an object in a lathe the
          motion of the face plate; a lathe dog.
      (b) A spool holder or bobbin holder in a braiding machine.
          (c) A movable piece in magazine guns which transfers
          the cartridge to a position from which it can be
          thrust into the barrel.
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   Carrier pigeon (Zool.), a variety of the domestic pigeon
      used to convey letters from a distant point to to its
      home.

   Carrier shell (Zool.), a univalve shell of the genus
      Phorus; -- so called because it fastens bits of stones
      and broken shells to its own shell, to such an extent as
      almost to conceal it.

   Common carrier (Law.) See under Common, a.
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