Meaning

originFrom Middle English bist, beest, best, from Old English bist ("(thou) art"; second person singular of bēon (“to be”)), from Proto-Germanic *biusi (“(thou) art”), equivalent to be + -est. Cognate with West Frisian bist (“(thou) art”), Low German büst (“(thou) art”), German bist (“(thou) art”).

Etymology from Wiktionary, CC BY-SA 3.0