10 letters · 18 points in Scrabble
adjective incapable of being placated
originFrom Middle English implācāble (“immitigable, unappeasable”) from Old French implacable (“harsh, unrelenting; implacable”) (modern French implacable), from Latin implācābilis (“unappeasable, implacable; irreconcilable”), from im- (variant of in- (prefix meaning ‘not’)) + plācābilis (“placable; appeasing, moderating, pacifying, propitiating; acceptable”) (from plācō (“to assuage, pacify, placate;…
Etymology from Wiktionary, CC BY-SA 3.0