n. The state or quality of being imperturbable. [ 1913 Webster ]
a. [ L. imperturbabilis; pref. im- not + perturbare to disturb: cf. F. imperturbable. See Perture. ] Incapable of being disturbed or disconcerted;
adv. In an imperturbable manner; calmly. C. Bronté. [ 1913 Webster ]