duty vs fealty

duty

noun
  • That which one is morally or legally obligated to do. 

  • The state of being at work and responsible for or doing a particular task. 

  • A tax placed on imports or exports; a tariff. 

  • The efficiency of an engine, especially a steam pumping engine, as measured by work done by a certain quantity of fuel; usually, the number of pounds of water lifted one foot by one bushel of coal (94 lbs. old standard), or by 1 cwt. (112 lbs., England, or 100 lbs., United States). 

fealty

noun
  • The oath by which this obligation was assumed. 

  • Fidelity to one's lord or master; the feudal obligation by which the tenant or vassal was bound to be faithful to his lord. 

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