moderator

One that moderates, as.

One that arbitrates or mediates.

One who presides over a meeting, forum, or debate.

The officer who presides over a synod or general assembly of the Presbyterian Church.

A substance, such as water or graphite, used in a nuclear reactor to decrease the speed of fast neutrons and increase the likelihood of fission.

In astrology, any one of the four principal points in a nativity upon which the native’s fortunes are supposed to depend: the sun, moon, ascendant, or mid-heaven.

In mech., a device for moderating or reducing the speed of an internal-combustion engine by the operation of a throttle-valve. Its action is the reverse of that of the accelerator.

One who or that which moderates, restrains, or represses.

In microscopy, a device used to diminish the intensity or vary the character of the light which illuminates the object: it consists commonly of a screen of opal glass, ground glass, or glass of a pale-blue or neutral tint.

An umpire; a judge.