moderator

noun

• 1an arbitrator or mediator:Egypt managed to assert its role as a regional moderator
• a presiding officer, especially a chairman of a debate: the debates will each feature one moderator and a panel of three questioners
• a Presbyterian minister presiding over an ecclesiastical body: the newly elected Moderator of the Dutch Reformed Church

• 2British a person who reviews examination papers to ensure consistency, or otherwise oversees an examination: after marking by the tutor, the papers are returned to a moderator

• 3a person who moderates an Internet message board or chat room.

• 4 Physics a substance used in a nuclear reactor to retard neutrons: in a fast reactor there is no moderator to slow the reaction down