[mod.er.a.tor] n (ca. 1560) 1: one who arbitrates: mediator
2: one who presides over an assembly, meeting, or discussion: as a: the presiding officer of a Presbyterian governing body b: the nonpartisan presiding officer of a town meeting c: the chairman of a discussion group
3: a substance (as graphite) used for slowing down neutrons in a nuclear reactor -- mod.er.a.tor.ship n