co-father vs genitor

co-father

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

genitor

noun
  • a biological parent (either male or female), or the direct cause of an offspring. 

  • a generator; an originator 

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