co-mother vs relative

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. 

relative

noun
  • Someone in the same family; someone connected by blood, marriage, or adoption. 

  • A type of adjective that inflects like a relative clause, rather than a true adjective, in certain Bantu languages. 

adj
  • Expressed in relation to another item, rather than in complete form. 

  • Having the same key but differing in being major or minor. 

  • Connected to or depending on something else; comparative. 

  • Depending on an antecedent; comparative. 

  • Relevant; pertinent; related. 

  • Capable to be changed by other beings or circumstance; conditional. 

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