co-mother vs uncle

co-mother

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

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

  • 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. 

uncle

noun
  • The brother or brother-in-law of one’s parent. 

  • A source of advice, encouragement, or help. 

  • Used as a fictive kinship title for a close male friend of one's parent or parents. 

  • The male cousin of one’s parent. 

  • Used as a title for the male companion to one's (usually unmarried) parent. 

  • An affectionate term for a man of an older generation than oneself, especially a friend of one's parents, by means of fictive kin. 

  • Any middle-aged or elderly man older than the speaker and/or listener. 

verb
  • To act like, or as, an uncle. 

  • To address somebody by the term uncle. 

intj
  • A cry used to indicate surrender. 

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