staggering vs unheard-of

staggering

adj
  • Incredible, overwhelming, amazing. 

  • Lurching, floundering. 

noun
  • The motion of one who staggers. 

  • The condition of being staggered or amazed. 

  • In animation, the repetition of a sequence of frames to show struggling effort 

unheard-of

adj
  • Previously unknown; unprecedented. 

  • Unknown or known to only few people. 

How often have the words staggering and unheard-of occurred in a corpus of books? (source: Google Ngram Viewer )