reasonable vs unheard-of

reasonable

adj
  • Just; fair; agreeable to reason. 

  • Satisfactory. 

  • Not excessive or immoderate; within due limits; proper. 

  • Not expensive; fairly priced. 

unheard-of

adj
  • Unknown or known to only few people. 

  • Previously unknown; unprecedented. 

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