Origin: Latin suffix -able
Unflappable has 2 different meanings across 1 category:
not easily perturbed or excited or upset; marked by extreme calm and composure
"hitherto imperturbable, he now showed signs of alarm"
"an imperturbable self-possession"
"unflappable in a crisis"
Remaining composed and level-headed at all times; impossible to fluster; not becoming frustrated or irritated easily.