"Call it a day," "Rome wasn’t built in a day," or "save it for a rainy day" are just some of the phrases you've used your whole life. But where did they actually come from? And what did they mean at the beginning? These everyday sayings may sound simple or ordinary, but each one carries a surprisingly rich history. For centuries, people have used the idea of a "day" to talk about work, time, patience, and life itself, long before any of us ever said them at the office or at the family dinner. Here, we explore the true origins and meanings behind 10 of the most familiar "day" idioms you still hear and say today.