12 letters · 23 points in Scrabble
adjective loud enough to shake the very earth
adjective sufficiently significant to affect the whole world
originFrom earth + shaking as a calque of Ancient Greek ἐννοσίγαιος (ennosígaios), ἐνοσίχθων (enosíkhthōn).
Etymology from Wiktionary, CC BY-SA 3.0