An Etymological Dictionary of the German Language/Ader
Ader, f., ‘vein,’ from MidHG. âder, OHG. âdara, f., ‘vein, sinew,’ corresponding to MidLG. ader, ‘vein, sinew,’ Du. ader, AS. œ̂dre, f., ‘vein’ (rarely êðr), OSw. aþra, ModSw. ådra; also without the deriv. r, OIc. œ̂ðr (the r is simply a nomin. suffix), f., ‘vein;’ the Goth. cognate êþ is not found. The pre-Teut. êt- has been connected with Gr. ἥτορ, ‘heart,’ ἦτρον, ‘abdomen,’ and here it must be recollected that MidHG. and MidLG. âder in the plur. may signify ‘bowels.’