formality vs impropriety

formality

noun
  • Something said or done as a matter of form. 

  • A specific requirement for obtaining a legal status, conducting a transaction, etc. 

  • A customary ritual without new or unique meaning. 

  • The state of being formal. 

impropriety

noun
  • The condition of being improper. 

  • An improper act. 

  • Improper language. 

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