Answer: unheardof

AnswerCrossword Clue
UNHEARDOF

Outrageous

UNHEARDOF

Without precedent

UNHEARDOF

Like the first ever

UNHEARDOF
Not even rare
UNHEARDOF
Simply not done
UNHEARDOFRarer than rare
UNHEARDOFWithout precedent.
UNHEARDOFTotally new.
UNHEARDOFUnprecedented
UNHEARDOFShocking, as behavior