有一天在英语中表示“一天”，可以说"one day"或"a day"。来源是拉丁语"diēs"，意为"白天"。例句：

One day, I'll be the best in the world at what I do.

A day without laughter is a day wasted.

One day you'll thank me for being so hard on you.

A day at the beach is the perfect way to relax and unwind.