duty vs sanction

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). 

sanction

noun
  • An approval, by an authority, generally one that makes something valid. 

  • A penalty, punishment, or some coercive measure, intended to ensure compliance; especially one adopted by several nations, or by an international body. 

  • A law, treaty, or contract, or a clause within a law, treaty, or contract, specifying any of the above. 

verb
  • To penalize (a state etc.) with sanctions. 

  • To ratify; to make valid. 

  • To give official authorization or approval to; to countenance. 

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