mod·er·a·tor / ˈmädəˌrātər/ • n. 1. an arbitrator or mediator: Egypt managed to assert its role as a regional moderator. ∎  a presiding officer, esp. a chairman of a debate. ∎  a Presbyterian minister presiding over an ecclesiastical body.2. Physics a substance used in a nuclear reactor to retard neutrons.DERIVATIVES: mod·er·a·tor·ship / -ˌship/ n.

moderator A person who controls a newsgroup, having the authority to warn users and block or remove messages if these are inappropriate.