Conductor

noun

1. One who conducts or leads; a guide; a director.
2. A person who conducts an orchestra, choir or other music ensemble; a professional whose occupation is conducting.
3. A person who takes tickets on public transportation and also helps passengers

   "train conductor; tram conductor"

4. Something that can transmit electricity, heat, light or sound.
5. An ideal of a ring that measures how far it is from being integrally closed