Word Origin & History late 14c., "hard, unbreakable," from
earlier noun (O.E. aðamans) meaning "a very hard stone," from L.
adamantem (nom. adamas), from Gk. adamas (gen. adamantos)
"unbreakable," the name of a hypothetical hardest material,
perhaps lit. "invincible," from a- "not" + daman "to conquer, to
tame" (see ), or else a word of foreign origin altered to
conform to Gk. Applied in antiquity to white sapphire, magnet
(perhaps via confusion with L. adamare "to love passionately"),
steel, emery stone, and especially diamond (see diamond ).
Figurative sense of "unshakeable" first recorded 1670s.