1520s, "one who leads or guides," from Middle French conductour (14c., Old French conduitor), from Latin conductor "one who hires, contractor," in Late Latin "a carrier," from conductus, past participle of conducere (see conduce).Earlier in same sense was conduitour (early 15c., from Old French conduitor). Meaning "leader of an orchestra or chorus" is from 1784; meaning "one who has charge of passengers and collects fares on a railroad" is 1832, American English. Physics sense of "object or device that passes heat" is from 1745; of electricity from 1737.