An Etymological Dictionary of the German Language/Annotated/Moder
Moder, masculine, ‘mud, mould, decay,’ from late Middle High German (Middle German) moder, masculine, ‘body that has been decomposed, decay, bog, moor’; compare Dutch modder, ‘slime,’ English mother, ‘slimy substance’ (especially in vinegar), Dutch moer, ‘yeast, lees.’ The entire class has become current only in the modern languages; compare the corresponding Middle German mot, ‘moor, morass, marsh,’ Middle English mudde, English mud. The early history of the cognates is obscure; Greek μυδών, ‘fungous flesh,’ on account of its permutation does not belong to the cognates.