n.
1.any substance used to slow down neutrons in nuclear reactors
2.in the Presdyterian church, the officer who presides over a synod or general assembly
3.someone who presides over a forum or debate
4.someone who mediates disputes and attempts to avoid violence
Idiom of the Day
in the nick of time
just in time, just before it is too late
I was able to answer the telephone just in the nick of time.