An Etymological Dictionary of the German Language/Annotated/be-

by Friedrich Kluge

be-, prefix from Middle High German be, properly a verbal prefix from Old High German and Gothic bi, which has no definite meaning; identical with the preposition bei, from Old High German and Middle High German bî (Gothic bi), Anglo-Saxon bî, English by. For be there appears a shorter syncopated form in bange, Erbarmen? barsch? bleiben, Block. See specially bei.