mourn vs rue

mourn

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

  • To utter in a sorrowful manner. 

  • To wear mourning. 

noun
  • Sorrow, grief. 

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

rue

verb
  • To repent of or regret (some past action or event); to wish that a past action or event had not taken place. 

noun
  • Any of various perennial shrubs of the genus Ruta, especially the herb Ruta graveolens (common rue), formerly used in medicines. 

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