Not easily excited, even under pressure
With her imperturbable calm she did not begin to speak in front of the valet.
During this time he went from one city to the other, according as the danger was more pressing, and constantly displayed an admirable zeal and an imperturbable energy.
It is not too much to say that his imperturbable equanimity, his serene bonhomie kept the host together.
Annoyed by Whitworth's imperturbable demeanour, he ended with these words: "You must respect treaties, then: woe to those who do not respect treaties.
His prudent reserve and imperturbable calmness were branded as stiffness and haughtiness.