at some time in the future, or on a particular day in the past :
One day, I want to leave the city and move to the country.
One day, he walked out of the house with a small bag and never came back.
at some time in the future, or on a particular day in the past :
One day, I want to leave the city and move to the country.
One day, he walked out of the house with a small bag and never came back.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005