imperturbable

adjective

अविचलित; शांत

not easily perturbed or excited or upset; marked by extreme calm and composure

hitherto imperturbable, he now showed signs of alarm
अब तक शांत रहने वाला वह अब घबराहट दिखाने लगा

an imperturbable self-possession
अविचलित आत्म-संयम