<p><strong>Adjective</strong></p><ul><li>not penetrable; that cannot be penetrated, pierced, entered, etc.</li><li>inaccessible to ideas, influences, etc.</li><li>incapable of being understood; inscrutable; unfathomable: an impenetrable mystery.</li></ul><p><strong>Synonyms</strong></p><ul><li>hidden</li><li>obscure</li><li>mysterious</li><li>incomprehensible</li></ul><p><strong>Antonyms</strong></p><ul><li>lucid</li><li>clear</li></ul>