Adamant

Ad"a*mant (ăd"ȧ*mănt), n. [OE. adamaunt, adamant, diamond, magnet, OF. adamant, L. adamas, adamantis, the hardest metal, fr. Gr. 'ada`mas, -antos; 'a priv. + dama^,n to tame, subdue. In OE., from confusion with L. adamare to love, be attached to, the word meant also magnet, as in OF. and LL. See Diamond, Tame.] 1. 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.

Opposed the rocky orb
Of tenfold adamant, his ample shield.
Milton.

2. Lodestone; magnet. [Obs.] "A great adamant of acquaintance." Bacon.

As true to thee as steel to adamant.
Greene.