moderator

noun

1. 1.Someone who moderates
2. 2.The person who presides over a synod of a Presbyterian Church
3. 3.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. 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. 5.An examiner at Oxford and Cambridge universities.