Firm; unshakeable; unyielding; determined.
Very difficult to break, pierce, or cut.
An embodiment of impregnable hardness.
An imaginary rock or mineral of impenetrable hardness; a name given to the diamond and other substances of extreme hardness.
Typical of an obstinate person; fixed and unmoving.
Stubbornly adhering to an opinion, purpose, or course, usually with implied unreasonableness; persistent.
Not easily subdued or removed.