adjective. Not willing to change one's opinion, purpose, or principles; unyielding.

noun. A stone once believed to be impenetrable in its hardness.

noun. An extremely hard substance.

noun. A name applied with more or less indefiniteness to various real or imaginary metals or minerals characterized by extreme hardness: as the diamond

noun. the natural opposite of the diamond

noun. a lodestone or magnet, and

noun. an anti-magnet.

noun. In general, any substance of impenetrable or surpassing hardness; that which is impregnable to any force.

noun. A stone imagined by some to be of impenetrable hardness; a name given to the diamond and other substances of extreme hardness; but in modern mineralogy it has no technical signification. It is now a rhetorical or poetical name for the embodiment of impenetrable hardness.

noun. Lodestone; magnet.

adjective. Firm; unshakeable; unyielding; determined.

noun. A rock or mineral held by some to be of impenetrable hardness; a name given to the diamond and other substances of extreme hardness.

noun. An embodiment of impregnable hardness.

noun. A magnet; a lodestone.

adjective. impervious to pleas, persuasion, requests, reason

noun. very hard native crystalline carbon valued as a gem