An Etymological Dictionary of the German Language/Blick
Blick, m., ‘glance, look, gleam,’ from MidHG. blick, ‘splendour, lightning, glance’; corresponds to OHG. blic (blicches), n., ‘lightning’ (also blicfiur, ‘electricity’). The orig. sense of the MidHG. word was probably heller Strahl (a bright flash), Strahl being used figuratively of the eye as of lightning; the physical meaning of the stem has been preserved in Blitz. The root is shown under blecken, and especially under Blitz, to be the pre-Teut. bhleg.