not easily upset or worried by a difficult situation; calm His normally imperturbable assistant burst into tears.
NAmE//ˌɪmpərˌtərbəˈbɪlət̮i//
noun [uncountable] NAmE//ˌɪmpərˈtərbəbli//
adverbSee imperturbable in the Oxford Advanced Learner's DictionaryCheck pronunciation: imperturbable