co-mother vs relation

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. 

relation

noun
  • A member of one's extended family; a relative. 

  • The manner in which two things may be associated. 

  • A set of ordered tuples. 

  • A set of ordered tuples retrievable by a relational database; a table. 

  • The act of intercourse. 

  • Specifically, a set of ordered pairs; a binary relation. 

  • The act of relating a story. 

  • A statement of equality of two products of generators, used in the presentation of a group. 

  • A subobject of a product of objects. 

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