Imperturbable

прилагательное невозмутимый, спокойный, хладнокровный Синоним(ы): calm, cool, dispassionate, sober, unruffled Антоним(ы): agitated, frantic, nervous, touchy, volatile

Большой англо-русский словарь

Imperturbable

adjective Etymology: Middle English, from Late Latin imperturbabilis, from Latin in- + perturbare to perturb marked by extreme calm, impassivity, and steadiness; serene Synonyms: see coolimperturbability nounimperturbably adverb

Merriam-Webster's Collegiate Dictionary