Antonyms for the phrase "let know" include keeping secret, concealing, withholding information, ignoring, and prohibiting. When someone doesn't let others know about certain information or keeps it secret, it can create confusion, mistrust, or even suspicion. Often, withholding information can result in missed opportunities or damage trust in relationships. Ignoring someone or disregarding their request for information can also cause frustration and resentment. Prohibiting or preventing someone from knowing something can feel like a violation of basic human rights. Therefore, it is important to understand the antonyms of "let know" and use them judiciously to maintain healthy and respectful communication.