adamant
/ˈæd.ə.mənt/noun
Definition
The hardest stone; probably diamond or corundum. Used figuratively to mean unyielding or impenetrable.
Modern Equivalent
hardest stone / diamond
Usage Notes
God made Ezekiel's forehead 'harder than flint, even as an adamant stone' to withstand the opposition of rebellious Israel.
Example Verse
“As an adamant harder than flint have I made thy forehead: fear them not, neither be dismayed at their looks, though they be a rebellious house.”Ezekiel 3:9