marécage m (plural marécages)
From Norman or Picard maresc, from Frankish *marisk (“marsh, swamp”), from Proto-Germanic *mariskaz (“marsh, swamp”), from Proto-Germanic *mari (“lake, sea, moor”), from Proto-Indo-European *mari-, *mori- (“sea”) + -age. Akin to Middle Dutch mersch, maersch (“marsh”), Middle Low German mersch, marsch (“marshland”), Old English merisc (“marsh”). More at marais, mare.