[mod-uh-rey-ter] 
| 1. | a person or thing that moderates. |
| 2. | a person who presides over a panel discussion on radio or television. |
| 3. | a presiding officer, as at a public forum, a legislative body, or an ecclesiastical body in the Presbyterian Church. |
| 4. | Physics. a substance, as graphite or heavy water, used to slow neutrons to speeds at which they are more efficient in causing fission. |
| moderator (mŏd'ə-rā'tər) Pronunciation Key
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. |
əˌreɪ