There are many synonyms for the phrase "holding your tongue," which means keeping quiet or refraining from speaking your mind. Some alternatives include "biting your lip," "keeping mum," "zipping your lips," "buttoning your lip," "holding your peace," and "keeping a lid on it." These phrases can be used in a variety of situations, such as when someone wants to avoid causing offense, when someone is trying to maintain a professional demeanor in a tense situation, or when someone simply wants to avoid saying something they may later regret. Regardless of the context, using one of these phrases can help convey the message that you are choosing to remain silent.