marsh vs fenland

marsh and fenland both are nouns.

Word	Noun	Adjective	Verb	Adverb
marsh	Yes	No	No	No
fenland	Yes	No	No	No

As nouns, marsh and fenland are synonyms defined as:

marsh and fenland: low-lying wet land with grassy vegetation; usually is a transition zone between land and water

Other synonyms of marsh include fen, marshland.

marsh (noun)	fenland (noun)
low-lying wet land with grassy vegetation; usually is a transition zone between land and water	low-lying wet land with grassy vegetation; usually is a transition zone between land and water