[{"Bold_text": "adjective", "List Items": ["not penetrable; that cannot be penetrated, pierced, entered, etc.", "inaccessible to ideas, influences, etc.", "incapable of being understood; inscrutable; unfathomable:an impenetrable mystery.Synonyms: hidden , obscure , mysterious , incomprehensible Antonyms: lucid , clear", "Physics.possessing impenetrability ."]}]