An Etymological Dictionary of the German Language/Lücke

by Friedrich Kluge

Lücke, f., ‘gap, chasm,’ from MidHG. lücke, lucke, OHG. lucka, from *luggja, f., ‘hole, gap,’ closely allied to locker (MidHG. loger, UpG. luck). The UpG. dials. contain a prim. form *luggia (Swiss lugg, not lukχ), hence OHG. luccha, ‘gap,’ is abnormal. For this reason too the phonetic relation of the word to Loch is obscure.