Any substance used to slow down neutrons in nuclear reactors.

Roget 174: moderation, lenity etc. 740; temperateness, gentleness etc. adj.; sobriety; quiet; mental calmness etc. (inexcitability) 826^†.    moderating etc. v.; anaphrodisia^†; relaxation, remission, mitigation, tranquilization^†, assuagement, contemporation^†, pacification.    measure, juste milieu [Fr.], golden mean, ariston metron [Gr.].    moderator; lullaby, sedative, lenitive, demulcent, antispasmodic, carminative, laudanum; rose water, balm, poppy, opiate, anodyne, milk, opium, poppy or mandragora;" wet blanket; palliative.    ... show more

Roget 423: luminary; light etc. 420; flame etc. (fire) 382.    spark, scintilla; phosphorescence, fluorescence.    sun, orb of day, Phoebus, Apollo^†, Aurora; star, orb; meteor, falling star, shooting star; blazing star, dog star, Sirius; canicula, Aldebaran^†; constellation, galaxy; zodiacal light; anthelion^†; day star, morning star; Lucifer; mock sun, parhelion; phosphor, phosphorus; sun dog^†; Venus.    aurora, polar lights; northern lights, aurora borealis; southern lights, aurora australis.    lightning; chain lightning, fork lightning, sheet lightning, summer lightning; ball lightning, kugelblitz [G.]; [chemical substances giving off light without burning] phosphorus, yellow phosphorus; scintillator, phosphor; firefly luminescence.    ignis fatuus [Lat.]; Jack o'lantern, Friar's lantern; will-o'-the-wisp, firedrake^†, Fata Morgana [Lat.]; Saint Elmo's fire.    [luminous insects] glowworm, firefly, June bug, lightning bug.    [luminous fish] anglerfish.    [Artificial light] gas; gas light, lime light, lantern, lanthorn^†; dark lantern, bull's-eye; candle, bougie [Fr.], taper, rushlight; oil etc. (grease) 356; wick, burner; Argand^†, moderator, duplex; torch, flambeau, link, brand; gaselier^†, chandelier, electrolier^†, candelabrum, candelabra, girandole^†, sconce, luster, candlestick.    [non-combustion based light sources] lamp, light; incandescent lamp, tungsten bulb, light bulb; flashlight, torch [Brit.]; arc light; laser; [microwave radiation]; maser neon bulb, neon sign; fluorescent lamp.    [parts of a light bulb] filament; socket; contacts; filler gas.    firework, fizgig^†; pyrotechnics; rocket, lighthouse etc. (signal) 550.    ... show more

Roget 694: director, manager, governor, rector, comptroller.    superintendent, supervisor, straw boss; intendant; overseer, overlooker^†; supercargo^†, husband, inspector, visitor, ranger, surveyor, aedile^†; moderator, monitor, taskmaster; master etc. 745; leader, ringleader, demagogue, corypheus, conductor, fugleman^†, precentor^†, bellwether, agitator; caporal^†, choregus^†, collector, file leader, flugelman^†, linkboy^†.    guiding star etc. (guidance) 693; adviser etc. 695; guide etc. (information) 527; pilot; helmsman; steersman, steermate^†; wire-puller.    driver, whip, Jehu, charioteer; coachman, carman, cabman; postilion, vetturino^†, muleteer, arriero^†, teamster; whipper in.    head, head man, head center, boss; principal, president, speaker; chair, chairman, chairwoman, chairperson; captain etc. (master) 745; superior; mayor etc. (civil authority) 745; vice president, prime minister, premier, vizier, grand vizier, eparch^†.    officer, functionary, minister, official, red-tapist^†, bureaucrat; man in office, Jack in office; office bearer; person in authority etc. 745.    statesman, strategist, legislator, lawgiver, politician, statist^†, statemonger^†; Minos, Draco; arbiter etc. (judge) 967; boss [U.S.], political dictator.    board etc. (council) 696.    secretary, secretary of state; Reis Effendi; vicar etc. (deputy) 759; steward, factor; agent etc. 758; bailiff, middleman; foreman, clerk of works; landreeve^†; factotum, major-domo^†, seneschal, housekeeper, shepherd, croupier; proctor, procurator.    ... show more

Roget 724: mediation, mediatorship^†, mediatization^†; intervention, interposition, interference, intermeddling, intercession; arbitration; flag of truce etc. 723; good offices, peace offering; parley, negotiation; diplomatics^†, diplomacy; compromise etc. 774.    [person who mediates] mediator, arbitrator, intercessor, peacemaker, makepeace^†, negotiator, go-between; diplomatist etc. (consignee) 758; moderator; propitiator; umpire.    ... show more

Polish: spowalniacz, moderator

In the Presbyterian church, the officer who presides over a synod or general assembly.

Someone who presides over a forum or debate.

Polish: przewodniczący

Someone who mediates disputes and attempts to avoid violence.

Dutch: moderator
Polish: mediator, moderator, rozjemca