From Proto-Germanic *mariskaz, from PIE *mori- (water) — literally 'the watery place,' sibling of Latin 'mare' (sea).
An area of low-lying land that is waterlogged and often dominated by grasses, reeds, and sedges; a wetland that is periodically or permanently flooded.
From Old English 'mersc' or 'merisc,' meaning a marsh or swamp, from Proto-Germanic *mariskaz, a derivative of *mari- ('sea, lake, body of water'), from PIE *mori- ('body of standing water, sea, lake'). The word thus literally means 'the sea-like place' or 'the watery place,' a formation that recognizes marshland as terrain defined by the persistent presence of water. The same PIE root gives Latin
The word 'marsh' is etymologically 'the place that is like the sea' — from the same root as Latin 'mare' (sea) and English 'mere' (lake). French 'marais' ('marsh, swamp') was borrowed from the Frankish Germanic form of the same word, making it a Germanic loanword hiding inside French — and it gave its name to the Marais district of Paris, once a genuine swamp.