7 letters · 10 points in Scrabble
noun very hard native crystalline carbon valued as a gem
adjective impervious to pleas, persuasion, requests, reason; ; - W.Churchill
originFrom Middle English adamant, adamaunt, from Latin adamantem, accusative singular form of adamās (“hard as steel”), from Ancient Greek ἀδάμαντ- (adámant-, “invincible”), oblique stem of ἀδάμας (adámas). Doublet of diamond.
Etymology from Wiktionary, CC BY-SA 3.0