BM vs defecation

BM

verb
  • To have a bowel movement. 

  • To use bad manners. 

defecation

noun
  • The act or process of voiding feces from the bowels. 

  • Any of several processes for the removal of impurities, or for clarifying various materials. 

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