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Related to moderator: Moderator variable
1. Presbyterian Church a minister appointed to preside over a Church court, synod, or general assembly
2. a presiding officer at a public or legislative assembly
3. a material, such as heavy water or graphite, used for slowing down neutrons in the cores of nuclear reactors so that they have more chance of inducing nuclear fission
4. an examiner at Oxford or Cambridge Universities in first public examinations
5. (in Britain and New Zealand) one who is responsible for consistency of standards in the grading of some educational assessments
6. a person who moniters the conversations in an on-line chatroom for bad language, inappropriate content, etc
The material used in a nuclear reactor to moderate or slow down neutrons from the high velocities at which they are created in the fission process.