An Etymological Dictionary of the German Language/Bocksbeutel
Bocksbeutel, m., ‘old prejudice,’ first occurs in ModHG., and connected instinctively by Germans with Bock; it is, however, of LG. origin, bocks- representing bôks (‘of the book’). The women of Hamburg used to carry their hymn-books at their side in a satchel, which they were always fond of wearing. When applied to a sort of bottle, Bocksbeutel has a different origin, and means properly ‘the scrotum of the buck.’