heirdom vs primogeniture

heirdom

noun
  • An inheritance or succession. 

primogeniture

noun
  • An instance of such a right of inheritance, established by custom or law. 

  • The principle that the eldest child, traditionally the eldest male, has an exclusive right of inheritance. 

  • The state of being the firstborn of the children of the same parents. 

How often have the words heirdom and primogeniture occurred in a corpus of books? (source: Google Ngram Viewer )