purgatory vs rue

purgatory

adj
  • Tending to cleanse; expiatory. 

noun
  • Any situation where suffering is endured, particularly as part of a process of redemption. 

rue

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

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

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