hypnic vs yawning

hypnic

adj

  • That induces sleep. 

noun

  • Any sleep-inducing drug. 

yawning

adj

  • That yawns or yawn. 

  • Wide open. 

noun

  • The action of the verb yawn. 

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