1. (noun) any substance used to slow down neutrons in nuclear reactors

• deuterium oxide
• heavy water

2. (noun) someone who mediates disputes and attempts to avoid violence

• modifier

1. (noun) any substance used to slow down neutrons in nuclear reactors

• inhibitor

2. (noun) in the Presbyterian church, the officer who presides over a synod or general assembly

• presiding officer

3. (noun) someone who presides over a forum or debate

• presiding officer

4. (noun) someone who mediates disputes and attempts to avoid violence

• go-between
• intercessor
• intermediary
• intermediator
• mediator

1. (noun) in the Presbyterian church, the officer who presides over a synod or general assembly

• moderatorship

2. (noun) someone who presides over a forum or debate

• chair
• lead
• moderate
• moderatorship

3. (noun) someone who mediates disputes and attempts to avoid violence

• chasten
• moderate
• temper
• moderatorship