<p><strong>Noun</strong></p><ul><li>a person or thing that moderates.</li><li>a person who presides over a panel discussion on radio or television.</li><li>a member of an online message board or electronic mailing list with privileges and responsibilities to approve or reject messages and uphold the terms of service.</li><li>a presiding officer, as at a public forum, a legislative body, or an ecclesiastical body in the Presbyterian Church.</li><li>Physics. a substance, as graphite or heavy water, used to slow neutrons to speeds at which they are more efficient in causing fission.</li></ul>