An Etymological Dictionary of the German Language/böse
böse, adj., from the equiv. MidHG. bœse, OHG. bôsi, ‘bad, useless, slanderous.’ A word peculiar to Germ., not found in the other dialects; the primary meaning, judging from OHG. bôsa, ‘buffoonery,’ bôsân, ‘to vilify,’ was probably ‘speaking malevolently.’ If -si- were regarded us a suffix, Gr. φαῦλος (perhaps for φαῦσ-λος), with the evolution of meaning ‘trifling, bad, wicked,’ would be connected with böse.