An Etymological Dictionary of the German Language/Rahm

by Friedrich Kluge

Rahm, m., ‘cream, crust of mould or mildew,’ from the equiv. MidHG. roum, m.; comp. Du. room, AS. reám (earlier ModE. ream), OIc. rjóme, ‘cream.’ The â of the ModHG. form compared with OHG. *roum (Thuring. roum) is dialectal (comp. MidHG. strâm and stroum under Strom). The origin of these cognates has not yet been discovered.