SINCE 1828
one day
idiomDefinition of one day
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.
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Merriam-Webster unabridged
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