Origin and history of conductor

1520s, "one who leads or guides," from French conductour (14c., Old French conduitor), from Latin conductor "one who hires, contractor," in Late Latin "a carrier," from conductus, past participle of conducere "to lead or bring together, contribute, serve," from assimilated form of com "with, together" (see con-) + ducere "to lead" (from PIE root *deuk- "to lead").

Earlier in same sense was conduitour (early 15c., from Old French conduitor). The meaning "a director or manager" is from 1630s; the specific sense of "leader of an orchestra or chorus" is attested by 1784.

The office of conductor in the modern sense was not clearly distinguished from that of leader until about 1800; formerly the leader played an instrument, usually the harpsichord [Century Dictionary]

 The meaning "one who has charge of passengers and collects fares on a railroad" is attested by 1832, American English.

The sense in modern physics of "object or device that passes heat or other energy" is by 1745; in reference to electricity from 1737.