inflexibleness vs rigidness

inflexibleness

noun
  • The quality or state of being inflexible 

  • Obstinacy of will or temper; firmness of purpose that will not yield to importunity or persuasion; unbending pertinacity. 

rigidness

noun
  • Rigidity. 

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