American Heritage® Dictionary of the English Language, Fourth
Edition - adj. Impervious to pleas, appeals, or reason;
stubbornly unyielding. See Synonyms at inflexible. - n. A stone
once believed to be impenetrable in its hardness. - n. An
extremely hard substance. Century Dictionary and Cyclopedia - n.
A name applied with more or less indefiniteness to various real
or imaginary metals or minerals characterized by extreme
hardness: as the diamond - n. the natural opposite of the
diamond - n. a lodestone or magnet, and - n. an anti-magnet. -
n. In general, any substance of impenetrable or surpassing
hardness; that which is impregnable to any force. - adj. Firm;
unshakeable; unyielding; determined. - n. A rock or mineral held
by some to be of impenetrable hardness; a name given to the
diamond and other substances of extreme hardness. - n. An
embodiment of impregnable hardness. - n. A magnet; a lodestone.
GNU Webster's 1913 - n. A stone imagined by some to be of
impenetrable hardness; a name given to the diamond