if a person or their expression is inscrutable, it is hard to know what they are thinking or feeling, because they do not show any emotion
NAmE//ɪnˌskrut̮əˈbɪlət̮i//
noun [uncountable] NAmE//ɪnˈskrut̮əbli//
adverbSee inscrutable in the Oxford Advanced Learner's DictionaryCheck pronunciation: inscrutable