known vs well-known

known

adj
  • Identified as a specific type; famous, renowned. 

  • Accepted, familiar, researched. 

noun
  • Any fact or situation which is known or familiar. 

  • A constant or variable the value of which is already determined. 

well-known

adj
  • Familiar, famous, renowned or widely known. 

  • Generally recognised; reserved for some usual purpose. 

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