An Etymological Dictionary of the German Language/Fenster
Fenster, n., ‘window,’ from the equiv. MidHG. vęnster, OHG. vęnstar, n.; comp. Du. venster, n. Based, with a curious change of gender, on Lat. fenestra, from which, however, the fęnstar of the Mid Europ. Teutons could only be produced by shifting the accent back according to the Teut. custom (comp. Abt) and by syncopating the second e. This indicates that the word was borrowed very early, in the beginning of the OHG. period. Yet the idea was well known to the older periods, as is testified by the terms naturally applied to the existing object — Goth. augadaurô, ‘eye-gate,’ AS. êgþŷrel, ‘eye-hole,’ OIc. vindauga (whence MidE. windôge, E. window). By the introduction of the Southern term (comp. also OIr. senister, W. ffenester) the idea was probably reconstructed. This word was borrowed at the same period as other words — Ziegel, Mauer — relating to the building of houses.