An Etymological Dictionary of the German Language/Geisel
Geisel (1.), m. and f., ‘hostage,’ from MidHG. gisel, OHG. gisal, m., n., ‘prisoner of war, person held in security’; corresponding to AS. gîsel, OIc. gîsl, m. To connect it with Geisel (2.), f., as if ‘hostage’ were lit. ‘one who is scourged,’ is impossible. It is, probably, most closely allied to the equiv. OIr. giall (for *gísal).
Geisel (2.) f., ‘scourge, whip,’ from the equiv. MidHG. geisel), OHG. geisala, geisla, f.; akin to OIc. geisl, geisle, m., ‘pole used by persons walking in snow-shoes.’ The stem gais- is connected with the OTeut. term gaiza-, ‘spear’ (see Ger). Hence ‘pole, staff,’ must be accepted as the prim. meaning; the second component is Goth. walus, ‘staff,’ so that OHG. geis-ala stands for *geis-wala, just as OHG. wurzala for AS. wyrt-walu (see under Wurzel).