co-father vs co-parent

co-father

noun
  • In a male homosexual couple, the nonbiological father (partner of the biological father) of a child. 

co-parent

noun
  • A parent in a same-sex couple. 

  • A godparent. 

  • A divorced or separated parent who shares custody with the other parent. 

  • Someone who shares in the parenting of a child or children, such as 

verb
  • To act as a co-parent; to share custody of a child or children; to share in the responsibility of parenting a child or children. 

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