"Keep mum" is an idiom used to describe the act of remaining silent or not revealing confidential information. There are several synonyms that can be used instead of "keep mum" such as "keep quiet," "stay silent," "keep a secret," "remain tight-lipped," or "maintain confidentiality." These synonyms convey the same meaning of not divulging sensitive information. In certain situations, it's essential to maintain discretion and keep mum to preserve the trust and integrity of the relationship. Whether it's personal or professional matters, using these synonyms can help you communicate effectively without betraying anyone's confidence. Ultimately, the key is to show good judgment and be mindful of the consequences of disclosing confidential information.