also: いっせいいちだい
noun, noun which may take the genitive case particle 'no'
once in a lifetime; the first and last occurrence of one's lifetime
A yojijukugo used for a unique, unrepeatable event or experience in a person's life. Often carries a dramatic or momentous tone.
This is a once-in-a-lifetime chance.
He stood on the biggest stage of his life.