前ぜん代だい未み聞もん

noun, noun which may take the genitive case particle 'no'

unprecedented; unheard-of; record-breaking

Emphasizes that something has never been heard of or seen before in history; often used in news for extraordinary events.

• これは前ぜん代だい未み聞もんの大だい災さい害がいだ。

  This is an unprecedented catastrophe.