Middle English bi- is from Old English be- (“be-”), from Proto-Germanic *bi- (“be-”), from Proto-Germanic *bi (“near, by”), ultimately from Proto-Indo-European *h₁epi (“at, near”). Compare also traitor, treason, tradition. The modern sense “to disclose, discover, reveal unintentionally” is due to influence from or merger with English bewray (“to reveal, divulge”), which is similar in sound and meaning. The similarity with German betrügen, Dutch bedriegen, from Proto-West Germanic *bidreugan (“to betray, deceive”), is coincidental.