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.
      [1913 Webster]

            Zeal, the blind conductor of the will. --Dryden.
      [1913 Webster]

   2. One in charge of a public conveyance, as of a railroad
      train or a street car. [U. S.]
      [1913 Webster]

   3. (Mus.) The leader or director of an orchestra or chorus.
      [1913 Webster]

   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.
      [1913 Webster]

   5. (Surg.) A grooved sound or staff used for directing
      instruments, as lithontriptic forceps, etc.; a director.
      [1913 Webster]

   6. (Arch.) Same as Leader.
      [1913 Webster]

   Prime conductor (Elec.), the largest conductor of an
      electrical machine, serving to collect, accumulate, or
      retain the electricity.
      [1913 Webster]

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.

Moby Thesaurus II by Grady Ward, 1.0:

107 Moby Thesaurus words for "conductor":
   Kapellmeister, Mahdi, administrator, agent, baggage man, bakehead,
   band leader, band major, bandmaster, bell cow, bell mare,
   bellwether, bodyguard, born leader, brakeman, brakie, butcher,
   cavalier, chaperon, charismatic leader, choirmaster, choragus,
   companion, conductance, conduction, conductivity, convoy,
   coryphaeus, deputy, dielectric, directeur, director, dispatcher,
   driver, drum major, duce, duenna, electric conduction, engineer,
   escort, esquire, fellow traveler, file leader, fireman,
   footplate man, forerunner, fugleman, functionary, gas conduction,
   governor, guard, handler, impresario, inspired leader, insulator,
   intendant, ionic conduction, leader, leader of men, lineman,
   liquid conduction, manager, manipulator, messiah,
   metallic conduction, mho, nonconductor, operant, operative,
   operator, orchestra leader, pacemaker, pacesetter, photoconduction,
   pilot, porter, precentor, producer, railroad man, railroader,
   rector, redcap, responsible person, ringleader, runner,
   safe-conduct, semiconductor, shepherd, smoke agent, squire,
   standard-bearer, stationmaster, steersman, stoker, supercargo,
   superconductivity, superconductor, swain, switchman,
   symphonic conductor, torchbearer, trainboy, trainman, trainmaster,
   usher, yardman, yardmaster