Defamatory is the describing word. A defamatory comment, article, caption, or post is one that writes or says bad or untrue things about someone so that people may think badly of them. The word sits on the statement, not on the person: a defamatory tweet, defamatory remarks — not he defamatory her. That doing-word is defame. Formal and legal. If something is true and said fairly, people will argue it is not defamatory; the fight is often about whether the words really harm a name, and whether they can be backed up.