callous vs unkind

callous

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

  • Having calluses, or relating to calluses. 

unkind

adj
  • Lacking kindness, sympathy, benevolence, gratitude, or similar; cruel, harsh or unjust; ungrateful. 

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