moderator

1. Someone who moderates.
2. An arbitrator or mediator.
3. The chair or president of a meeting, etc.
4. A person who enforces the rules of a discussion forum by deleting posts, banning users, etc.
5. The person who presides over a synod of a Presbyterian church.
6. A substance (often water or graphite) used to decrease the speed of fast neutrons in a nuclear reactor and hence increase likelihood of fission.
7. A device used to deaden some of the noise from a firearm, although not to the same extent as a suppressor or silencer.
8. A mechanical arrangement for regulating motion in a machine, or producing equality of effect.

Plural moderators