corvee vs socage

corvee

noun
  • Unpaid labor required by a feudal lord. 

  • Labor, especially for roads or dams, in lieu of taxes. 

socage

noun
  • In the Middle Ages (and chiefly but not exclusively medieval England), a legal system whereby a tenant would pay a rent or do some agricultural work for the landlord. 

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