Definition & Meaning of "[unring] (the|a) bell"

What is the origin of the idiom "unring the bell" and when to use it?

The phrase is thought to have originated in the 19th century, when bells were used to signal important events. If someone rang a bell to announce a wedding, for example, it would be impossible to unring the bell and undo the event. The idiom "unring the bell" refers to the idea that once something has been said or done, it cannot be undone or unsaid. It is often used to describe a situation where a mistake has been made or a secret has been revealed, and the damage cannot be undone.