12 letters · 20 points in Scrabble
adverb in an obvious and provable manner
originEtymology tree English demonstrable Proto-Indo-European *leyg-der. Proto-Germanic *līkąder. Proto-Germanic *-līkaz Proto-Germanic *-ê Proto-Germanic *-līkê Proto-West Germanic *-līkē Old English -līċe Middle English -ly English -ly English demonstrably From demonstrable + -ly. First attested in the early 17th century.
Etymology from Wiktionary, CC BY-SA 3.0