(Hebrews shamir), Ezek. 3:9. The Greek word adamas means diamond. This stone is not referred to, but corundum or some kind of hard steel. It is an emblem of firmness in resisting adversaries of the truth (Zechariah 7:12), and of hard-heartedness against the truth (Jeremiah 17:1).

Noah Webster's New International Dictionary of the English Language

1. (n.) Unyielding in opinion; also a stone or diamond perceived 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.

2. (n.) Lodestone; magnet.