SM vs spanking

SM

symbol
  • service mark 

spanking

noun
  • An incident of such punishment, or such physical act in a non-punitive context, such as a birthday spanking. 

  • A form of physical punishment in which a beating is applied to the buttocks. 

adv
  • An intensifier. 

adj
  • Fast and energetic. 

  • Brisk and fresh. 

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