1. imperturbable - Adjective
2. imperturbable - Adjective Satellite
not easily perturbed or excited or upset; marked by extreme calm and composure
Source: WordNetThe feeling that we call "I" seems to define our point of view in every moment, and it also provides an anchor for popular beliefs about souls and freedom of will. And yet this feeling, however imperturbable it may appear at present, can be altered, interrupted, or entirely abolished. Sam Harris
hitherto imperturbable, he now showed signs of alarm Source: Internet
an imperturbable self-possession Source: Internet
unflappable in a crisis Source: Internet