9 letters · 18 points in Scrabble
adjective (usually used with `to') occurring or existing without the knowledge of
adverb without someone's knowledge
originEtymology tree English un- Proto-Indo-European *h₁ep-der. Proto-Indo-European *h₁épsder. Proto-Indo-European *h₁epider. Proto-Indo-European *h₁pi Proto-Germanic *bider. Proto-Germanic *bi- Proto-West Germanic *bi- Old English be- Middle English bi- English be- English known English beknown English unbeknown From un- + beknown.
Etymology from Wiktionary, CC BY-SA 3.0