imperturbability vs restraint

imperturbability

noun
  • A state of calm, unruffled self-assurance; aplomb, composure. 

restraint

noun
  • something that restrains, ties, fastens or secures 

  • control or caution; reserve 

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