arduousness vs felicity

arduousness

noun
  • The state of being arduous. 

felicity

noun
  • Something that is either a source of happiness or particularly apt. 

  • An apt and pleasing style in speech, writing, etc.; (countable) an apt and pleasing choice of words. 

  • Happiness; (countable) an instance of this. 

  • Reproduction of a sign with fidelity. 

  • Good luck; success; (countable) An instance of unexpected good luck; a stroke of luck; also, a lucky characteristic. 

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