有一天用英语怎么说

"How to say 'one day' in English?"

In English, "one day" is a simple phrase that refers to an unspecified future time. It can be used in a variety of contexts to express the idea of something happening at some point in the future. For example, "One day, I hope to travel the world" or "One day, she might become a famous musician." This phrase is often used in storytelling or making general statements about the future.