An Etymological Dictionary of the German Language/Galgen
Galgen, m., ‘gallows, gibbet, crossbeam,’ from MidHG. galge, OHG. galgo, m., ‘gallows (also applied to the cross of Christ), frame over a well from which the bucket is hung to draw water.’ It corresponds to OSax. galgo, Du. galg, AS. gealga, E. gallows (the plur. used as a sing., yet comp. gallow-tree), OIc. galge, ‘gallows,’ Goth. galga, m. (applied to the cross of Christ, as also in all the other OTeut. dialects); a common Teut. word, Teut. galgan-, pre-Teut. ghalgha-; comp. Lith. żalga, f., ‘pole.’ Note the double sense of the MidHG. and OHG. word. Probably some such idea as a ‘long pliable rod’ is the starting-point of the various meanings of the cognates.