co-mother vs godmother

co-mother

noun
  • In a lesbian couple, the nonbirth mother (partner of the birth mother) of a child, especially one who takes an equal role in mothering the child. 

  • In polygamy, the relationship between one co-wife and another, in respect to their children. 

  • In polygamy, a wife of one's father who is not one's mother; that is, co-wife of one's mother. 

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. 

How often have the words co-mother and godmother occurred in a corpus of books? (source: Google Ngram Viewer )