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a person or thing that moderates

Presbyterian Church a minister appointed to preside over a Church court, synod, or general assembly

a presiding officer at a public or legislative assembly

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

an examiner at Oxford or Cambridge Universities in first public examinations

(in Britain and New Zealand) one who is responsible for consistency of standards in the grading of some educational assessments

a person who monitors the conversations in an on-line chatroom for bad language, inappropriate content, etc

A substance, such as graphite, water, or heavy water, placed in a nuclear reactor to slow neutrons down to speeds at which they are more likely to be captured by fissionable components of a fuel (such as uranium-235) and less likely to be absorbed by nonfissionable components of a fuel (such as uranium-238).

Also called neutron moderator

See also slow neutron