/ ɪnˈskruːtəbl; NAmE / adjective
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
► in·scrut·abil·ity / ɪnˌskruːtəˈbɪləti; NAmE / noun [ U ]
► in·scrut·ably / ɪnˈskruːtəbli; NAmE / adverb
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WORD ORIGIN
late Middle English : from ecclesiastical Latin inscrutabilis , from in- not + scrutari to searchto search (originally sort rubbish, from scruta rubbish).