To vilify someone is to spread nasty stories about them, whether true or not.
The verb vilify comes from the same root as the word vile and is a negative word if ever there was one! One way to remember the word is to think about how it sounds — like the word villain (which is unrelated and comes from villa). This suggests that when you vilify someone, you make them sound villainous. So avoid spreading vile words that vilify another and make him or her seem like a villain.