fenland vs marsh

fenland and marsh both are nouns.

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

As nouns, fenland and marsh are synonyms defined as:

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

Other synonyms of fenland include fen, marshland.

fenland (noun)	marsh (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