serene vs unflappable

serene

adj
  • Without worry or anxiety; unaffected by disturbance. 

  • Used as part of certain titles, originally to indicate sovereignty or independence. 

  • Calm, peaceful, unruffled. 

noun
  • Serenity; clearness; calmness. 

  • A fine rain from a cloudless sky after sunset. 

verb
  • To make serene. 

unflappable

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

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