moderator: Meaning and Definition of

mod•er•a•tor

1. a person or thing that moderates.
2. a person who presides over a panel discussion on radio or television.
3. a presiding officer, as at a public forum, a legislative body, or an ecclesiastical body in the Presbyterian Church.
4. a substance, as graphite or heavy water, used to slow neutrons to speeds at which they are more efficient in causing fission.