used to describe sth special that is not likely to happen to you again :
An opportunity like this comes once in a lifetime.
a once-in-a-lifetime experience
used to describe sth special that is not likely to happen to you again :
An opportunity like this comes once in a lifetime.
a once-in-a-lifetime experience
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005