imperturbable

 
Pronunciation: /ˌɪmpəˈtəːbəb(ə)l/

adjective

  • unable to be upset or excited; calm: an imperturbable tranquillity

Derivatives

imperturbability

Pronunciation: /-ˈbɪlɪti/
noun

imperturbably

adverb

Origin:

late Middle English: from late Latin imperturbabilis, from in- 'not' + perturbare (see perturb)