An Etymological Dictionary of the German Language/Loch
Loch, n., ‘hole, dungeon, haunt,’ from MidHG. loch, n., OHG. loh, gen. lohhes, n., ‘enclosed place, prison, lurking-place, cave, hole, opening.’ Comp. AS. loc, n., ‘enclosed place, lock’; loca, m., ‘enclosed place, prison’; from the former E. lock is derived. The various meanings all originate in ‘enclosed place’; comp. Goth. usluka-, ‘opening.’ The subst. is formed by gradation from an old Teut. vb. (obsolete in ModHG.), MidHG. lûchen, OHG. lûhhan, Goth. lûkan, AS. lûcan, ‘to lock,’ which may be compared (since the Pre-Teut. root is lū̆g) with Lith. lúżtu (lúżti), ‘to be broken,’ as well as with Sans. ruj, ‘to break.’