9 letters · 15 points in Scrabble
adjective (followed by `of') lacking capacity or ability
adjective not being susceptible to or admitting of something (usually followed by `of')
adjective (followed by `of') not having the temperament or inclination for
originBorrowed from Middle French incapable, equivalent to in- + capable.
Etymology from Wiktionary, CC BY-SA 3.0