decorum vs propriety

decorum

noun
  • Appropriate social behavior. 

  • A convention of social behavior. 

propriety

noun
  • Correctness in behaviour and morals; good manners, seemliness. 

  • The fact of possessing something; ownership. 

  • Suitability, fitness; the quality of being appropriate. 

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