mom vs stepmother

mom

noun
  • Mother. 

  • An adult female owner of a pet. 

verb
  • To care for in a motherly way. 

stepmother

noun
  • The wife of one's biological father, other than one's biological mother. 

  • A viola, especially Viola tricolor, heartsease. 

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