moderator

Etymology

Learned borrowing from Latin moderātor. First attested as Middle English moderatour.

noun

1. Someone who moderates.
   1. An arbitrator or mediator.
   2. The chair or president of a meeting, etc.
   3. (Internet) A person who enforces the rules of a discussion forum by deleting posts, banning users, etc.
2. The person who presides over a synod of a Presbyterian Church.
3. (nuclear physics) A substance (often water or graphite) used to decrease the speed of fast neutrons in a nuclear reactor and hence increase likelihood of fission.
4. A device used to deaden some of the noise from a firearm, although not to the same extent as a suppressor or silencer.
5. (UK) An examiner at Oxford and Cambridge universities.
   One hall called Civil Law Hall or School, flouriſhed about this time (though in its buildings decayed) by the care of the learned and judicious Dr. Will. Warham Principal or Moderator thereof […] 1792, Anthony à Wood, The History and Antiquities of the University of Oxford: In Two Books, volume 1, Oxford: John Gutch, →OCLC, page 661
6. (Ireland) At the University of Dublin, either the first (senior) or second (junior) in rank in an examination for the degree of Bachelor of Arts.
7. (UK) Someone who supervises and monitors the setting and marking of examinations by different people to ensure consistency of standards.
8. A mechanical arrangement for regulating motion in a machine, or producing equality of effect.
9. (historical) A kind of lamp in which the flow of the oil to the wick is regulated.