9 letters · 14 points in Scrabble
noun a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth
originFrom Ancient Greek λανθάνω (lanthánō, “to escape notice”) + -um (“a chemical element”), because it had gone long undetected in mineral ores.
Etymology from Wiktionary, CC BY-SA 3.0