unheard-of vs usual

unheard-of

adj
  • Previously unknown; unprecedented. 

  • Unknown or known to only few people. 

usual

adj
  • Most commonly occurring; typical. 

noun
  • A specific good or service (e.g. a drink) that someone typically orders. 

  • The typical state of something, or something that is typical. 

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