Perhaps from optanomai (through the idea of the shading or proximity to the organ of vision); the eye-"brow" or forehead, i.e. (figuratively) the brink of a precipice -- brow.
KJV: And rose up, and thrust him out of the city, and led him unto the brow of the hill whereon their city was built, that they might cast him down headlong.
NASB: and they got up and drove Him out of the city, and led Him to the brow of the hill on which their city had been built, in order to throw Him down the cliff.