relation vs relative-in-law

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. 

relative-in-law

noun
  • Co-relative-in-law: A relative of one's generation, separated by two degrees of marriage. 

  • A relative of one's generation, separated by one degree of marriage. 

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