An Etymological Dictionary of the German Language/Annotated/Rain
Rain, masculine, ‘strip or belt of grass as a dividing line between fields, ridge,’ from Middle High German and Old High German rein, masculine, ‘ridge’ (as a line of division between fields); corresponding to Low German reen, ‘field boundary,’ Old Icelandic rein, feminine, ‘strip of land.’ Perhaps cognate with Sanscrit rêkhâ, feminine, ‘row, line, strip.’