noun, noun which may take the genitive case particle 'no'
unprecedented and unrepeatable; first and last
Used for events or things so extraordinary (either wonderful or terrible) that nothing like it has happened before and probably never will again. Often appears in news or dramatic descriptions.
That athlete's record is unprecedented and unlikely to be broken.
これは空前絶後の大災害と言われている。
This is said to be a disaster of unprecedented and unrepeatable scale.