Blab out is a phrasal verb that means to disclose information that should have been kept secret. Antonyms of blab out include "keep mum", "hold back", "conceal", and "remain quiet". Keeping mum suggests keeping silent and not revealing any information, while holding back means restraining oneself from sharing confidential information. The word "conceal" implies hiding something intentionally, and "remain quiet" signifies not speaking at all. These antonyms are essential for individuals who have to deal with sensitive information or those who are required to maintain confidentiality in their professions. Therefore, it is crucial to know the antonyms of blab out to effectively communicate without revealing confidential information.