one day
fixed phr..fixed phr.. A phrase used to talk about a time in the future that isn't specific. It can also mean a particular day in the past when you are telling a story.
fixed phr.. An adverbial phrase of time referring to an unspecified point in the future or a particular but unnamed day in the past, often used to begin a narrative.
One day, I want to own a dog.
She dreams that one day she will travel the world and see the pyramids.
One day, long after the memory of the argument had faded, he found the letter she had written and finally understood her reasons.
This phrase usually appears at the beginning or end of a sentence.
Contrast 'one day' (indefinite future/past) with 'someday' (indefinite future only) and 'the other day' (specific, recent past).
On one day, I will be famous.One day, I will be famous.When used to mean 'someday', this phrase does not require a preposition like 'on' or 'in'.