An Etymological Dictionary of the German Language/Annotated/Tadel
Tadel, masculine, ‘blame, censure, reproof,’ from Middle High German tadel, masculine and neuter, ‘fault, stain, defect (bodily or mental). The word is recorded at a remarkably late period — the end of the 12th century — but this, of course, does not prove that it was borrowed. The Teutonic root daþ (dad?) contained in it has been compared, probably without just grounds, with Greek τωθάω (root dhôdh), ‘to deride, mock.’