Detraction is saying something against another person that is not true--spreading falsehood against one's neighbor.
Calumny is harming another's reputation by saying something that is, nevertheless, true.
Both are sins against the 8th commandment and both are discouragingly easy to do.
They are also both sins against peace. If we are to have peace we are to be peace. It is difficult, but everything is possible through the grace of God.
Our Lady, Queen of Peace,
Pray for us!