Slander

Slander, synonymous with calumny, is a sin against the Eighth Commandment. It occurs when someone, by remarks contrary to the truth, harms the reputation of others and gives occasion for false judgments concerning them (CCC 2477).

A Grave Injustice

A person's reputation is a valuable asset, and deliberately destroying it with lies is a grave injustice. Like theft, slander incurs a moral obligation to make restitution—the slanderer must attempt to repair the damage done to the victim's good name (CCC 2487).