An Etymological Dictionary of the German Language/Fittich
Fittich, m., from the equiv. MidHG. vittich, vëttach, m., n., vëttache, f., m., ‘wing, pinion,’ OHG. fëtah, older fëthdhah, m.; in meaning a collective of Feder; comp. OSax. fëtherac, OHG. fëderah, MidHG. fëdrach, ‘wing’; the formation of OHG. fëthdhah is not clear; was the Goth. form *fiþþaks? The dentals are obscure, yet the word is undoubtedly related to Feder.