XXX vs improper

XXX

adj
  • Extra strong; very high quality. 

  • Designating extreme or hardcore pornography. 

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

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). 

noun
  • Triple X syndrome. 

improper

adj
  • unsuitable to needs or circumstances; inappropriate; inapt 

  • Not properly named; See, for example, improper fraction 

  • Not in keeping with conventional mores or good manners; indecent or immodest 

  • Not consistent with established facts; incorrect 

  • Of a complex random variable, correlated with its conjugate 

  • Not according to facts; inaccurate or erroneous 

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