co-father vs dad

co-father

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

dad

noun
  • A father, a male parent. 

  • A lump or piece. 

  • A blow; act of striking something. 

  • Used to address an older adult male 

  • Used to address one's father 

verb
  • To throw against something; to dash. 

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