moderator

noun12

1. •
   Someone who moderates.

   • Angling was […] a moderator of passions. — 1653
2. •
   The chair or president of a meeting, etc.
3. •
   The person who presides over a synod of a Presbyterian church.
4. •
   (Internet) A person who enforces the rules of a discussion forum by deleting posts, banning users, etc.
5. •
   (UK) Someone who supervises and monitors the setting and marking of examinations by different people to ensure consistency of standards.
6. •
   An arbitrator or mediator.
7. •
   A substance (often water or graphite) used to decrease the speed of fast neutrons in a nuclear reactor and hence increase likelihood of fission.
8. •
   A device used to deaden some of the noise from a firearm, although not to the same extent as a suppressor or silencer.
9. •
   A mechanical arrangement for regulating motion in a machine, or producing equality of effect.
10. •
    (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
11. •
    (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.
12. •
    (historical) A kind of lamp in which the flow of the oil to the wick is regulated.