Kotoba 千載一遇 vs 一世一代!

This week we are going to look at two expressions which more or less mean the same thing:

1.
千載一遇　せんざいいちぐう　senzaiichiguu = once in a lifetime (opportunity), (a golden opportunity that may) happen only once in a thousand years

2.
一世一代　いっせいいちだい　isseiichidai or いっせいちだい　isseichidai = once in a lifetime, the first and last occurrence (event, experience) of one’s lifetime

Both are common expressions used today. Although the younger generation opt not to use it, as more and more foreign loanwords enter the Japanese dictionary. The word チャンス　(chansu = chance, opportunity) is perhaps easier to remember and now a common J-lingo.