lifetime

once-in-a-lifetime chance and once-in-a-lifetime opportunity

a chance that will never occur again in one's lifetime. This is a once-in-a-lifetime chance. Don't miss it. She offered me a once-in-a-lifetime opportunity, but I turned it down.

See also: chance

---

once in a lifetime

only likely to happen once in someone's life Opportunities to play in the Cup Final only come once in a lifetime so we've got to make the most of it.

See also: once

Why break the habit of a lifetime?  (British & Australian humorous)

something that you say which means that you do not believe that someone will stop doing something bad that they have done all their lives 'I must stop writing my essays the night before the deadline.' 'Why break the habit of a lifetime?'

See make or break

See also: break, habit, why