obdurate vs unhelpful

obdurate

adj
  • Hardened against feeling; hard-hearted. 

  • Stubbornly persistent, generally in wrongdoing; refusing to reform or repent. 

unhelpful

adj
  • Not providing help or assistance; not helpful. 

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