An Etymological Dictionary of the German Language/Eisen
Eisen, n., ‘iron, weapon, sword, fetters,’ from MidHG. and MidLG. îsen (îsern), OHG. îsan, îsarn, n., ‘iron’; corresponds to Du. ijzer, AS. îsern, îren, E. iron, OIc. ísarn, Goth. eisarn, ‘iron.’ Its relation to Eis is still undecided; it is most closely connected with OIr. íarn, ‘iron’ (for *ísarno-), whence OIc. jarn (Dan. jern) is borrowed. It is less certain that OHG. êr, Goth. aiz, Lat. aes, ‘bronze,’ are allied to it. The deriv. r of the earlier forms is retained by ModHG. eisern, which is based on MidHG. îserîn, îsernîn, OHG. îsarnîn, adj., ‘of iron.’