The Collaborative International Dictionary of English v.0.48:

Conductor \Con*duct"or\ (k[o^]n*d[u^]k"t[~e]r), n. [LL., a
   carrier, transporter, L., a lessee.]
   1. One who, or that which, conducts; a leader; a commander; a
      guide; a manager; a director.
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            Zeal, the blind conductor of the will. --Dryden.
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   2. One in charge of a public conveyance, as of a railroad
      train or a street car. [U. S.]
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   3. (Mus.) The leader or director of an orchestra or chorus.
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   4. (Physics) A substance or body capable of being a medium
      for the transmission of certain forces, esp. heat or
      electricity; specifically, a lightning rod.
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   5. (Surg.) A grooved sound or staff used for directing
      instruments, as lithontriptic forceps, etc.; a director.
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   6. (Arch.) Same as Leader.
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   Prime conductor (Elec.), the largest conductor of an
      electrical machine, serving to collect, accumulate, or
      retain the electricity.
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WordNet (r) 3.0 (2006):

conductor
    n 1: the person who leads a musical group [syn: conductor,
         music director, director]
    2: a substance that readily conducts e.g. electricity and heat
       [ant: dielectric, insulator, nonconductor]
    3: the person who collects fares on a public conveyance
    4: a device designed to transmit electricity, heat, etc.