An Etymological Dictionary of the German Language/Annotated/gediegen
gediegen, adjective, ‘solid, pure, concise, pithy,’ from Middle High German gedigen, adjective, ‘adult, firm, hard, clear, pure,’ Old High German gidigan, adjective, ‘aged, advanced in years, earnest, pure, chaste’; properly a participle of gidihan (g by a grammatical change is the necessary form of h in the participle); Anglo-Saxon preserves the older participial form of the e-gradation, geþungen, ‘complete,’ so too Old Saxon thungan.