An Etymological Dictionary of the German Language/derb
derb, adj., ‘compact, stout, blunt, uncouth,’ derived in form from MidHG. dërp (b), ‘unleavened,’ but blended in meaning with a word derbe, derb, ‘worthy, honest’ (see bieder), deduced from OHG. and MidHG. bidérbe. MidHG. dërp, OHG. dërb, ‘unleavened,’ are equiv to OIc. þjarfr, AS. þeorf, E. therf. Bieder is related to bedürfen, but derb, ‘unleavened,’ on account of its meaning, cannot belong to the same stem; it is connected rather with the root verderben.