one day

idiom

1

: at some time in the future

One day, it'll happen. You'll see.

People may one day be able to take vacations to the moon.

2

: on a day in the past

I went to her house one day and had lunch with her.

One day, we had a terrible argument.

Examples of one day in a Sentence

Recent Examples on the Web

Last week, San Francisco broke a daily record for rain that had been in place since 1887, with a pounding 2.53 inches of rain falling in one day, according to the National Weather Service. —Christopher Cann, USA TODAY, 10 Feb. 2025

Typically, Black Friday extends for several weeks in today's world and lasts longer than one day. —Ashlyn Needham, Southern Living, 9 Feb. 2025

He’s continued writing a poem or two most nights since then and has amassed a collection of more than 100, which may one day become a book. —Jared Kaufman, Twin Cities, 8 Feb. 2025

The lawsuit comes one day after the U.S. Department of Justice sued Chicago and the state of Illinois over their sanctuary laws. —Shawna Chen, Axios, 7 Feb. 2025