in ‧ scru ‧ ta ‧ ble /ɪnˈskruːtəb ə l/ BrE AmE adjective
[ Date: 1500-1600 ; Language: Late Latin ; Origin: inscrutabilis , from Latin scrutari 'to search' ]
someone who is inscrutable shows no emotion or reaction in the expression on their face so that it is impossible to know what they are feeling or thinking:
He stood silent and inscrutable.
—inscrutably adverb
—inscrutability /ɪnˌskruːtəˈbɪləti, ɪnˌskruːtəˈbɪlɪti/ noun [uncountable]