extraordinary vs unusual

extraordinary

adj
  • Not ordinary; exceptional; unusual. 

  • Remarkably good. 

  • Special or supernumerary. 

noun
  • Anything that goes beyond what is ordinary. 

unusual

adj
  • Not usual, out of the ordinary. 

noun
  • Something that is unusual; an anomaly. 

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