XXX vs porn

XXX

noun
  • Triple X syndrome. 

adj
  • Extra strong; very high quality. 

  • Designating extreme or hardcore pornography. 

symbol
  • An indicator of hazard or poison. 

  • Traditional brewer's mark for barrels of extra strong beer—extended to other alcoholic beverages and other products having an extra strong dimension (varying from laundry soap to pornography). 

verb
  • To delete; to cross out, especially to conceal or suggest vulgar language. 

porn

noun
  • Material, usually visual, presenting something desirable in a sensational manner. 

  • A pornographic work. 

  • Material that provides illicit gratification of an obsessive or unhealthy interest in something. 

  • Pornography. 

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