nonplussed vs unflappable

nonplussed

adj
  • Unaffected, unfazed; unimpressed. 

  • Unsure how to act or respond; bewildered, perplexed. 

unflappable

adj
  • Remaining composed and level-headed at all times; impossible to fluster; not becoming frustrated or irritated easily. 

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