godmother vs stepmother

godmother

noun
  • A woman present at the christening of a baby who promises to help raise the child in a Christian manner; a female godparent who sponsors the baptism of a child. 

verb
  • To act as godmother to. 

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 godmother and stepmother occurred in a corpus of books? (source: Google Ngram Viewer )