due vs duty

due

noun
  • That which is owed; debt; that which belongs or may be claimed as a right; whatever custom, law, or morality requires to be done, duty. 

  • Deserved acknowledgment. 

  • Right; just title or claim. 

  • A membership fee. 

adj
  • Appropriate. 

  • Owing; ascribable, as to a cause. 

  • Owed or owing. 

  • Scheduled; expected. 

  • On a direct bearing, especially for the four points of the compass 

  • Having reached the expected, scheduled, or natural time. 

adv
  • Directly; exactly. 

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). 

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