rue vs ruefulness

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. 

ruefulness

noun
  • The property of being rueful. 

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