An Etymological Dictionary of the German Language/Annotated/Posse
Posse, feminine, ‘drollery, fun, farce,’ first occurs in early Modern High German; corresponding to Dutch poets, pots. Old High German gibôsi, ‘tricks, nugae’ (compare böse), cannot be allied to it. In earlier Modern High German Posse also signified the decoration, the accessories in works of art; hence the word has been connected with French ouvrage à bosse, ‘work in relief’ (compare Italian bozzo, ‘rough stone, stone blocks,’ bozzetto, ‘slight sketch’; also English bosh?).