callous vs hardened

callous

adj
  • Having calluses, or relating to calluses. 

  • Emotionally hardened; unfeeling and indifferent to the suffering/feelings of others. 

hardened

adj
  • Unfeeling; pitiless; callous. 

  • Inured; toughened. 

  • Firmly established or unlikely to change; inveterate. 

  • Having extra defences against attack; highly fortified. 

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