Found just one time in the New Testament (Rom. 12:20), the Greek word “anthrax” described “coal.”
When Christians are treated unkindly or unjustly, they are to do good to those who oppose them or their work. Repaying evil with good causes “coals of fire” (i.e. things like shame and regret) to be heaped upon a Christian’s enemies. Paul knew that some of the greatest weapons Christians have are things like love, kindness, and goodness.