mourn vs regret

mourn

verb
  • To utter in a sorrowful manner. 

  • To express sadness or sorrow for; to grieve over (especially a death). 

  • To wear mourning. 

noun
  • Sorrow, grief. 

  • A ring fitted upon the head of a lance to prevent wounding an adversary in tilting. 

regret

verb
  • To feel sorry about (any thing). 

  • To feel sorry about (a thing that has or has not happened), afterthink: to wish that a thing had not happened, that something else had happened instead. 

noun
  • Emotional pain on account of something done or experienced in the past, with a wish that it had been different; a looking back with dissatisfaction or with longing. 

  • The amount of avoidable loss that results from choosing the wrong action. 

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