"Keep lid on" means to control or suppress a situation or information. The antonyms for this phrase are to reveal or expose. When someone keeps a lid on something, they are not disclosing what is truly happening or sharing important details. To reveal or expose means to make something known or public. For instance, in a legal case, a lawyer might want to keep a lid on the evidence so that the other party does not use it against them. Conversely, a journalist might need to reveal the evidence to educate the public and hold those accountable who are responsible.