An Etymological Dictionary of the German Language/Annotated/Kahm
Kahm, Kahn, masculine, ‘mould on fermented liquids,’ from the equivalent Middle High German kâm (kân); compare Icelandic kám, neuter, ‘thin coating of dust, dirt,’ English coom, ‘soot, coal dust’ (with i mutation, English keam, keans); Gothic *kema-, *kemi-. The root ka- is inferred from Middle High German ka-del, masculine, ‘soot, dirt.’ Derivative ̣kahmig, adjective, ‘mouldy’ (of wine).