<p><strong>Adjective</strong></p><ul><li>utterly unyielding in attitude or opinion in spite of all appeals, urgings, etc.</li><li>too hard to cut, break, or pierce.</li></ul><p><strong>Noun</strong></p><ul><li>any impenetrably or unyieldingly hard substance.</li><li>a legendary stone of impenetrable hardness, formerly sometimes identified with the diamond.</li></ul><p><strong>End of Response</strong></p>