noun

• One who conducts or leads; a guide; a director.
• (music) A person who conducts an orchestra, choir or other music ensemble; a professional whose occupation is conducting.
• (rail transport) A person who takes tickets on public transportation and also helps passengers.
• (physics) Something that can transmit electricity, heat, light, or sound.
• (mathematics) An ideal of a ring that measures how far it is from being integrally closed
• A grooved sound or staff used for directing instruments, such as lithontriptic forceps; a director.
• (architecture) A leader.