An Etymological Dictionary of the German Language/Annotated/deftig

by Friedrich Kluge

deftig, adjective, Modern High German only, from Low German destig; the latter, with English daft, Anglo-Saxon gedœft, ‘mild, meek, gentle’ (Gothic gadaban, ‘to be fitting’), and perhaps with High German tapfer, is derived from a Teutonic root dab, dap. See tapfer.