一いっ世せ一いち代だい

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.

• これは一いっ世せ一いち代だいのチャンスだ。

  This is a once-in-a-lifetime chance.

• 彼かれは一いっ世せ一いち代だいの大だい舞ぶ台たいに立たった。

  He stood on the biggest stage of his life.